Gayatri Vedantam

Interests

Research

Bacterial pathogenesis, clinical microbiology, antibiotic resistance, healthcare-associated infections

Teaching

Bacterial pathogenesis, clinical microbiology, science career mentoring

Courses

Scholarly Contributions

Journals/Publications

• Anwar, F., Clark, M., Lindsey, J., Claus-Walker, R., Mansoor, A., Nguyen, E., Billy, J., Lainhart, W., Shehab, K., Viswanathan, V. K., & Vedantam, G. (2023). Prevalence of diagnostically-discrepant clinical specimens: insights from longitudinal surveillance. Frontiers in Medicine, 10, 1238159.
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  Infection (CDI) is a healthcare-associated diarrheal disease prevalent worldwide. A common diagnostic algorithm relies on a two-step protocol that employs stool enzyme immunoassays (EIAs) to detect the pathogen, and its toxins, respectively. Active CDI is deemed less likely when the Toxin EIA result is negative, even if the pathogen-specific EIA is positive for We recently reported, however, that low-toxin-producing strains recovered from Toxin-negative ('discrepant') clinical stool specimens can be fully pathogenic, and cause lethality in a rodent CDI model. To document frequency of discrepant CDI specimens, and evaluate strain diversity, we performed longitudinal surveillance at a Southern Arizona tertiary-care hospital.
• Tillotson, G., Vedantam, G., Shin, J. H., & Warren, C. A. (2023). The Importance of a Broad Consortium of Bacteria for a Healthy Gastrointestinal tract: A Narrative Review of the Live Biotherapeutic Product REBYOTA. Open Forum of Infectious Diseases, 10(11), ofad529.
• Weninger, S. N., Herman, C., Meyer, R. K., Beauchemin, E. T., Kangath, A., Lane, A. I., Martinez, T. M., Hasneen, T., Jaramillo, S. A., Lindsey, J., Vedantam, G., Cai, H., Cope, E. K., Caporaso, J. G., & Duca, F. A. (2023). Oligofructose improves small intestinal lipid-sensing mechanisms via alterations to the small intestinal microbiota. Microbiome, 11(1), 169.
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  Upper small intestinal dietary lipids activate a gut-brain axis regulating energy homeostasis. The prebiotic, oligofructose (OFS) improves body weight and adiposity during metabolic dysregulation but the exact mechanisms remain unknown. This study examines whether alterations to the small intestinal microbiota following OFS treatment improve small intestinal lipid-sensing to regulate food intake in high fat (HF)-fed rats.
• Anwar, F., & Vedantam, G. (2022). Surface-displayed glycopolymers of Clostridioides difficile. Current opinion in microbiology, 66, 86-91.
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  Clostridioides difficile is a leading cause of the healthcare-associated disease C. difficile infection (CDI), which has an annual US burden of over 200 000 cases. CDI mitigation strategies have been complicated by the emergence, and widespread distribution, of phylogenetically diverse lineages, as well as pathogen recalcitrance to genetic manipulation. In this review, we highlight past and current efforts to elucidate C. difficile surface glycopolymer biology since these molecules are essential for colonization, disease, and immunity elicitation, and may therefore have potential as CDI anti-infective targets.
• Anwar, F., Roxas, B. A., Shehab, K. W., Ampel, N. M., Viswanathan, V. K., & Vedantam, G. (2022). Low-toxin RT027 strains exhibit robust virulence. Emerging microbes & infections, 11(1), 1982-1993.
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  is a leading cause of healthcare-associated infections worldwide. Currently, there is a lack of consensus for an optimal diagnostic method for infection (CDI). Multi-step diagnostic algorithms use enzyme immunosorbent analysis (EIA)-based detection of toxins TcdA/TcdB in stool, premised on the rationale that EIA toxin-negative (Tox) patients have less severe disease and shorter diarrhoea duration. The aim of this study was to characterize toxigenic (i.e. -positive) strains isolated from diarrheic patient stool with an EIA Tox (i.e. "discrepant") CDI diagnostic test result. Recovered strains were DNA fingerprinted (ribotyped), subjected to multiple toxin, genome and proteome evaluations, and assessed for virulence. Overall, of 1243 -positive patient stool specimens from Southern Arizona hospitals, 31% were discrepant. For RT027 (the most prevalent ribotype)-containing specimens, 34% were discrepant; the corresponding RT027 isolates were cytotoxic to cultured fibroblasts, but their total toxin levels were comparable to, or lower than, the historic low-toxin-producing strain CD630. Nevertheless, these low-toxin RT027 strains (LT-027) exhibited similar lethality to a clade-matched high-toxin RT027 strain in Golden Syrian hamsters, and heightened colonization and persistence in mice. Genomics and proteomics analyses of LT-027 strains identified unique genes and altered protein abundances, respectively, relative to high-toxin RT027 strains. Collectively, our data highlight the robust virulence of LT-027 , provide a strong argument for reconsidering the clinical significance of a Tox EIA result, and underscore the potential limitations of current diagnostic protocols.
• Clark, A. E., Adamson, C. C., Carothers, K. E., Roxas, B. A., Viswanathan, V. K., & Vedantam, G. (2022). The Alternative Sigma Factor SigL Influences Toxin Production, Sporulation, and Cell Surface Properties. Frontiers in microbiology, 13, 871152.
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  The alternative sigma factor SigL (Sigma-54) facilitates bacterial adaptation to the extracellular environment by modulating the expression of defined gene subsets. A homolog of the gene encoding SigL is conserved in the diarrheagenic pathogen . To explore the contribution of SigL to biology, we generated -disruption mutants () in strains belonging to two phylogenetically distinct lineages-the human-relevant Ribotype 027 (strain BI-1) and the veterinary-relevant Ribotype 078 (strain CDC1). Comparative proteomics analyses of mutants and isogenic parental strains revealed lineage-specific SigL regulons. Concomitantly, loss of SigL resulted in pleiotropic and distinct phenotypic alterations in the two strains. Sporulation kinetics, biofilm formation, and cell surface-associated phenotypes were altered in CDC1 relative to the isogenic parent strain but remained unchanged in BI-1 . In contrast, secreted toxin levels were significantly elevated only in the BI-1 mutant relative to its isogenic parent. We also engineered SigL overexpressing strains and observed enhanced biofilm formation in the CDC1 background, and reduced spore titers as well as dampened sporulation kinetics in both strains. Thus, we contend that SigL is a key, pleiotropic regulator that dynamically influences 's virulence factor landscape, and thereby, its interactions with host tissues and co-resident microbes.
• Roxas, J. L., Ramamurthy, S., Cocchi, K., Rutins, I., Harishankar, A., Agellon, A., Wilbur, J. S., Sylejmani, G., Vedantam, G., & Viswanathan, V. K. (2022). Enteropathogenic Escherichia coli regulates host-cell mitochondrial morphology. Gut microbes, 14(1), 2143224.
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  The diarrheagenic pathogen enteropathogenic is responsible for significant childhood mortality and morbidity. EPEC and related attaching-and-effacing (A/E) pathogens use a type III secretion system to hierarchically deliver effector proteins into host cells and manipulate epithelial structure and function. Subversion of host mitochondrial biology is a key aspect of A/E pathogen virulence strategy, but the mechanisms remain poorly defined. We demonstrate that the early-secreted effector EspZ and the late-secreted effector EspH have contrasting effects on host mitochondrial structure and function. EspZ interacts with FIS1, a protein that induces mitochondrial fragmentation and mitophagy. Infection of epithelial cells with either wildtype EPEC or an isogenic deletion mutant (Δ) robustly upregulated FIS1 abundance, but a marked increase in mitochondrial fragmentation and mitophagy was seen only in Δinfected cells. FIS1-depleted cells were protected against Δinduced fission, and EspZ-expressing transfected epithelial cells were protected against pharmacologically induced mitochondrial fission and membrane potential disruption. Thus, EspZ interacts with FIS1 and blocks mitochondrial fragmentation and mitophagy. In contrast to WT EPEC, Δinfected epithelial cells had minimal FIS1 upregulation and exhibited hyperfused mitochondria. Consistent with the contrasting impacts on organelle shape, mitochondrial membrane potential was preserved in Δinfected cells, but profoundly disrupted in Δinfected cells. Collectively, our studies reveal hitherto unappreciated roles for two essential EPEC virulence factors in the temporal and dynamic regulation of host mitochondrial biology.
• Tzou, D. T., Stern, K. L., Duty, B. D., Hsi, R. S., Canvasser, N. E., De, S., Wong, A. C., Royal, C. R., Sloss, M. L., Ziemba, J. B., Harper, J. D., Bechis, S. K., Zampini, A. M., Borofsky, M. S., Bell, J. R., Friedlander, J. I., Leavitt, D. A., Nevo, A., Patel, N. D., , Patel, R. M., et al. (2022). Heterogeneity in stone culture protocols and endourologist practice patterns: a multi-institutional survey. Urolithiasis, 51(1), 15.
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  Kidney stone cultures can be beneficial in identifying bacteria not detected in urine, yet how stone cultures are performed among endourologists, under what conditions, and by what laboratory methods remain largely unknown. Stone cultures are not addressed by current clinical guidelines. A comprehensive REDCap electronic survey sought responses from directed (n = 20) and listserv elicited (n = 108) endourologists specializing in kidney stone disease. Questions included which clinical scenarios prompt a stone culture order, how results influence post-operative antibiotics, and what microbiology lab protocols exist at each institution with respect to processing and resulting stone cultures. Logistic regression statistical analysis determined what factors were associated with performing stone cultures. Of 128 unique responses, 11% identified as female and the mean years of practicing was 16 (range 1-46). A specific 'stone culture' order was available to only 50% (64/128) of those surveyed, while 32% (41/128) reported culturing stone by placing a urine culture order. The duration of antibiotics given for a positive stone culture varied, with 4-7 days (46%) and 8-14 days (21%) the most reported. More years in practice was associated with fewer stone cultures ordered, while higher annual volume of percutaneous nephrolithotomy was associated with ordering more stone cultures (p 
• Roxas, B. A., Roxas, J. L., Claus-Walker, R., Harishankar, A., Mansoor, A., Anwar, F., Jillella, S., Williams, A., Lindsey, J., Elliott, S. P., Shehab, K. W., Viswanathan, V. K., & Vedantam, G. (2020). Phylogenomic analysis of Clostridioides difficile ribotype 106 strains reveals novel genetic islands and emergent phenotypes. Scientific reports, 10(1), 22135.
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  Clostridioides difficile infection (CDI) is a major healthcare-associated diarrheal disease. Consistent with trends across the United States, C. difficile RT106 was the second-most prevalent molecular type in our surveillance in Arizona from 2015 to 2018. A representative RT106 strain displayed robust virulence and 100% lethality in the hamster model of acute CDI. We identified a unique 46 KB genomic island (GI1) in all RT106 strains sequenced to date, including those in public databases. GI1 was not found in its entirety in any other C. difficile clade, or indeed, in any other microbial genome; however, smaller segments were detected in Enterococcus faecium strains. Molecular clock analyses suggested that GI1 was horizontally acquired and sequentially assembled over time. GI1 encodes homologs of VanZ and a SrtB-anchored collagen-binding adhesin, and correspondingly, all tested RT106 strains had increased teicoplanin resistance, and a majority displayed collagen-dependent biofilm formation. Two additional genomic islands (GI2 and GI3) were also present in a subset of RT106 strains. All three islands are predicted to encode mobile genetic elements as well as virulence factors. Emergent phenotypes associated with these genetic islands may have contributed to the relatively rapid expansion of RT106 in US healthcare and community settings.
• Stewart, D., Anwar, F., & Vedantam, G. (2020). Anti-virulence strategies for infection: advances and roadblocks. Gut microbes, 12(1), 1802865.
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  infection (CDI) is a common healthcare- and antibiotic-associated diarrheal disease. If mis-diagnosed, or incompletely treated, CDI can have serious, indeed fatal, consequences. The clinical and economic burden imposed by CDI is great, and the US Centers for Disease Control and Prevention has named the causative agent, (CD), as an Urgent Threat To US healthcare. CDI is also a significant problem in the agriculture industry. Currently, there are no FDA-approved preventives for this disease, and the only approved treatments for both human and veterinary CDI involve antibiotic use, which, ironically, is associated with disease relapse and the threat of burgeoning antibiotic resistance. Research efforts in multiple laboratories have demonstrated that non-toxin factors also play key roles in CDI, and that these are critical for disease. Specifically, key CD adhesins, as well as other surface-displayed factors have been shown to be major contributors to host cell attachment, and as such, represent attractive targets for anti-CD interventions. However, research on anti-virulence approaches has been more limited, primarily due to the lack of genetic tools, and an as-yet nascent (but increasingly growing) appreciation of immunological impacts on CDI. The focus of this review is the conceptualization and development of specific anti-virulence strategies to combat CDI. Multiple laboratories are focused on this effort, and the field is now at an exciting stage with numerous products in development. Herein, however, we focus only on select technologies (Figure 1) that have advanced near, or beyond, pre-clinical testing (not those that are currently in clinical trial), and discuss roadblocks associated with their development and implementation.
• Maseda, D., Zackular, J. P., Trindade, B., Kirk, L., Roxas, J. L., Rogers, L. M., Washington, M. K., Du, L., Koyama, T., Viswanathan, V. K., Vedantam, G., Schloss, P. D., Crofford, L. J., Skaar, E. P., & Aronoff, D. M. (2019). Nonsteroidal Anti-inflammatory Drugs Alter the Microbiota and Exacerbate Colitis while Dysregulating the Inflammatory Response. mBio, 10(1).
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  infection (CDI) is a major public health threat worldwide. The use of nonsteroidal anti-inflammatory drugs (NSAIDs) is associated with enhanced susceptibility to and severity of CDI; however, the mechanisms driving this phenomenon have not been elucidated. NSAIDs alter prostaglandin (PG) metabolism by inhibiting cyclooxygenase (COX) enzymes. Here, we found that treatment with the NSAID indomethacin prior to infection altered the microbiota and dramatically increased mortality and the intestinal pathology associated with CDI in mice. We demonstrated that in -infected animals, indomethacin treatment led to PG deregulation, an altered proinflammatory transcriptional and protein profile, and perturbed epithelial cell junctions. These effects were paralleled by increased recruitment of intestinal neutrophils and CD4 cells and also by a perturbation of the gut microbiota. Together, these data implicate NSAIDs in the disruption of protective COX-mediated PG production during CDI, resulting in altered epithelial integrity and associated immune responses. infection (CDI) is a spore-forming anaerobic bacterium and leading cause of antibiotic-associated colitis. Epidemiological data suggest that use of nonsteroidal anti-inflammatory drugs (NSAIDs) increases the risk for CDI in humans, a potentially important observation given the widespread use of NSAIDs. Prior studies in rodent models of CDI found that NSAID exposure following infection increases the severity of CDI, but mechanisms to explain this are lacking. Here we present new data from a mouse model of antibiotic-associated CDI suggesting that brief NSAID exposure prior to CDI increases the severity of the infectious colitis. These data shed new light on potential mechanisms linking NSAID use to worsened CDI, including drug-induced disturbances to the gut microbiome and colonic epithelial integrity. Studies were limited to a single NSAID (indomethacin), so future studies are needed to assess the generalizability of our findings and to establish a direct link to the human condition.
• Roxas, J. L., Monasky, R. C., Roxas, B. A., Agellon, A. B., Mansoor, A., Kaper, J., Vedantam, G., & Viswanathan, V. (2018). RhoGTPase Inhibition Contributes to Enteropathogenic Escherichia coli EspH-Induced Desmosomal Perturbations. Cellular and Molecular Gastroenterology and Hepatology.
• Roxas, J. L., Vedantam, G., & Viswanathan, V. K. (2018). Epithelial maturity influences EPEC-induced desmosomal alterations. Gut Microbes, 1-5.
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  Desmosomes are junctional protein complexes that confer strong adhesive capacity to adjacent host cells. In a recent study, we showed that enteropathogenic Escherichia coli (EPEC) disrupts desmosomes, weakens cell-cell adhesion and perturbs barrier function of intestinal epithelial (C2) cells. Desmosomal damage was dependent on the EPEC effector protein EspH and its inhibitory effect on Rho GTPases. EspH-mediated Rho inactivation resulted in retraction of keratin intermediate filaments and degradation of desmosomal cadherins. Immunofluorescence studies of EPEC-infected C2 cells revealed keratin retraction towards the nucleus coincident with significant cytoplasmic redistribution of the desmosomal cadherin desmoglein-2 (DSG2). In this addendum, we expand on how EPEC-induced keratin retraction leads to loss of DSG2 anchoring at the junctions, and show that maturity of the epithelial cell monolayer impacts the fate of desmosomes during infection.
• Vedantam, G., Kochanowsky, J., Lindsey, J., Mallozzi, M., Roxas, J. L., Adamson, C., Anwar, F., Clark, A., Claus-Walker, R., Mansoor, A., McQuade, R., Monasky, R. C., Ramamurthy, S., Roxas, B., & Viswanathan, V. K. (2018). An Engineered Synthetic Biologic Protects Against Infection. Frontiers in Microbiology, 9, 2080.
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  Morbidity and mortality attributed to infection (CDI) have increased over the past 20 years. Currently, antibiotics are the only US FDA-approved treatment for primary infection, and these are, ironically, associated with disease relapse and the threat of burgeoning drug resistance. We previously showed that non-toxin virulence factors play key roles in CDI, and that colonization factors are critical for disease. Specifically, a adhesin, Surface Layer Protein A (SlpA) is a major contributor to host cell attachment. In this work, we engineered Syn-LAB 2.0 and Syn-LAB 2.1, two synthetic biologic agents derived from lactic acid bacteria, to stably and constitutively express a host-cell binding fragment of the adhesin SlpA on their cell-surface. Both agents harbor conditional suicide plasmids expressing a codon-optimized chimera of the lactic acid bacterium's cell-wall anchoring surface-protein domain, fused to the conserved, highly adherent, host-cell-binding domain of SlpA. Both agents also incorporate engineered biocontrol, obviating the need for any antibiotic selection. Syn-LAB 2.0 and Syn-LAB 2.1 possess positive biophysical and properties compared with their parental antecedents in that they robustly and constitutively display the SlpA chimera on their cell surface, potentiate human intestinal epithelial barrier function , are safe, tolerable and palatable to Golden Syrian hamsters and neonatal piglets at high daily doses, and are detectable in animal feces within 24 h of dosing, confirming robust colonization. In combination, the engineered strains also delay (in fixed doses) or prevent (when continuously administered) death of infected hamsters upon challenge with high doses of virulent . Finally, fixed-dose Syn-LAB ameliorates diarrhea in a non-lethal model of neonatal piglet enteritis. Taken together, our findings suggest that the two synthetic biologics may be effectively employed as non-antibiotic interventions for CDI.
• Chu, M., Mallozzi, M. J., Roxas, B. P., Bertolo, L., Monteiro, M. A., Agellon, A., Viswanathan, V. K., & Vedantam, G. (2016). A Clostridium difficile Cell Wall Glycopolymer Locus Influences Bacterial Shape, Polysaccharide Production and Virulence. PLoS pathogens, 12(10), e1005946.
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  Clostridium difficile is a diarrheagenic pathogen associated with significant mortality and morbidity. While its glucosylating toxins are primary virulence determinants, there is increasing appreciation of important roles for non-toxin factors in C. difficile pathogenesis. Cell wall glycopolymers (CWGs) influence the virulence of various pathogens. Five C. difficile CWGs, including PSII, have been structurally characterized, but their biosynthesis and significance in C. difficile infection is unknown. We explored the contribution of a conserved CWG locus to C. difficile cell-surface integrity and virulence. Attempts at disrupting multiple genes in the locus, including one encoding a predicted CWG exporter mviN, were unsuccessful, suggesting essentiality of the respective gene products. However, antisense RNA-mediated mviN downregulation resulted in slight morphology defects, retarded growth, and decreased surface PSII deposition. Two other genes, lcpA and lcpB, with putative roles in CWG anchoring, could be disrupted by insertional inactivation. lcpA- and lcpB- mutants had distinct phenotypes, implying non-redundant roles for the respective proteins. The lcpB- mutant was defective in surface PSII deposition and shedding, and exhibited a remodeled cell surface characterized by elongated and helical morphology, aberrantly-localized cell septae, and an altered surface-anchored protein profile. Both lcpA- and lcpB- strains also displayed heightened virulence in a hamster model of C. difficile disease. We propose that gene products of the C. difficile CWG locus are essential, that they direct the production/assembly of key antigenic surface polysaccharides, and thereby have complex roles in virulence.
• Kullin, B., Brock, T., Rajabally, N., Anwar, F., Vedantam, G., Reid, S., & Abratt, V. (2016). Characterisation of Clostridium difficile strains isolated from Groote Schuur Hospital, Cape Town, South Africa. European journal of clinical microbiology & infectious diseases : official publication of the European Society of Clinical Microbiology, 35(10), 1709-18.
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  The C. difficile infection rate in South Africa is concerning. Many strains previously isolated from diarrhetic patients at Groote Schuur Hospital were ribotype 017. This study further characterised these strains with respect to their clonal relationships, antibiotic susceptibility, toxin production and various attributes impacting on pathogen colonisation. Multilocus variable-number tandem-repeat analysis (MLVA) was used to characterise all C. difficile isolates. Antibiotic susceptibility was determined by E-test and PCR-based analysis of the ermB, gyrA and gyrB genes. Auto-aggregation of cells was measured in broth, and biofilm formation observed in 24-well plates. Toxins were measured using the Wampole C DIFF TOX A/B II kit. Most isolates belonged to the ribotype 017 group. Identical MLVA types occurred in different wards over time, and several patients were infected with identical strains. All isolates were susceptible to vancomycin and metronidazole, but some ribotype 017 isolates showed reduced metronidazole susceptibility (≥2 mg l(-1)). Sixty-nine percent of ribotype 017 isolates were resistant to moxifloxacin, and 94 % to erythromycin, compared to 0 % and 17 % resistance, respectively, in non-ribotype 017 isolates. The ermB gene and mutations in the gyrA and/or gyrB genes were linked to erythromycin and moxifloxacin resistance, respectively. Ribotype 017 isolates auto-aggregated more strongly than other isolates and produced lower levels of the TcdB toxin than a reference strain. Certain strains produced strong biofilms. Patient-to-patient transfer and unique infection events could cause the predominance of ribotype 017 strains in the cohort. Multi-drug resistant strains are a potential reservoir for future infections.
• Pantaleon, V., Soavelomandroso, A., Bouttier, S., Briandet, R., Roxas, B., Chu, M., Collignon, A., Janoir, C., Vedantam, G., & Candela, T. (2015). The Clostridium difficile protease Cwp84 modulates both biofilm formation and cell-surface properties. PLoS One.
• Wilbur, J. S., Byrd, W., Ramamurthy, S., Ledvina, H., Khirfan, K., Riggs, M., Boedeker, E., Vedantam, G., & Viswanathan, V. K. (2015). The secreted effector protein EspZ is essential for virulence of rabbit enteropathogenic Escherichia coli. Infection and Immunity.
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  Attaching and effacing (A/E) pathogens adhere intimately to intestinal enterocytes and efface brush border microvilli. A key virulence strategy of A/E pathogens is the type III secretion system (T3SS)-mediated delivery of effector proteins into host cells. The secreted protein EspZ is postulated to promote enterocyte survival by regulating the T3SS and/or by modulating epithelial signaling pathways. To explore the role of EspZ in A/E pathogen virulence, we generated an isogenic espZ deletion strain (ΔespZ), and corresponding cis-complemented derivatives, of rabbit enteropathogenic Escherichia coli, and compared their ability to regulate the T3SS and influence host cell survival in vitro. For virulence studies, rabbits infected with these strains were monitored for bacterial colonization, clinical signs and intestinal tissue alterations. Consistent with earlier reports, espZ-transfected epithelial cells were refractory to infection-dependent effector translocation. Also, compared to the parent and complemented strains, ΔespZ induced greater host cell death. In the rabbit infections, fecal ΔespZ levels were ten-fold lower than the parent strain one day post-infection, while the complemented strain was recovered at intermediate levels. In contrast to the parent and complemented mutants, ΔespZ fecal carriage progressively decreased on subsequent days. ΔespZ-infected animals gained weight steadily over the infection period, failed to show characteristic disease symptoms, and displayed minimal infection-induced histological alterations. TUNEL staining of intestinal sections revealed increased epithelial cell apoptosis on Day 1 post-infection with ΔespZ, as compared to animals infected with the parent or complemented strains. Thus, EspZ-dependent host-cell cytoprotection likely prevents epithelial cell death and sloughing and, thereby, promotes bacterial colonization.
• Wilbur, J. S., Byrd, W., Ramamurthy, S., Ledvina, H., Khirfan, K., Riggs, M., Boedeker, E., Vedantam, G., & Viswanathan, V. K. (2015). The secreted effector protein EspZ is essential for virulence of rabbit enteropathogenic Escherichia coli. Infection and immunity.
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  Attaching and effacing (A/E) pathogens adhere intimately to intestinal enterocytes and efface brush border microvilli. A key virulence strategy of A/E pathogens is the type III secretion system (T3SS)-mediated delivery of effector proteins into host cells. The secreted protein EspZ is postulated to promote enterocyte survival by regulating the T3SS and/or by modulating epithelial signaling pathways. To explore the role of EspZ in A/E pathogen virulence, we generated an isogenic espZ deletion strain (ΔespZ), and corresponding cis-complemented derivatives, of rabbit enteropathogenic Escherichia coli, and compared their ability to regulate the T3SS and influence host cell survival in vitro. For virulence studies, rabbits infected with these strains were monitored for bacterial colonization, clinical signs and intestinal tissue alterations. Consistent with earlier reports, espZ-transfected epithelial cells were refractory to infection-dependent effector translocation. Also, compared to the parent and complemented strains, ΔespZ induced greater host cell death. In the rabbit infections, fecal ΔespZ levels were ten-fold lower than the parent strain one day post-infection, while the complemented strain was recovered at intermediate levels. In contrast to the parent and complemented mutants, ΔespZ fecal carriage progressively decreased on subsequent days. ΔespZ-infected animals gained weight steadily over the infection period, failed to show characteristic disease symptoms, and displayed minimal infection-induced histological alterations. TUNEL staining of intestinal sections revealed increased epithelial cell apoptosis on Day 1 post-infection with ΔespZ, as compared to animals infected with the parent or complemented strains. Thus, EspZ-dependent host-cell cytoprotection likely prevents epithelial cell death and sloughing and, thereby, promotes bacterial colonization.
• Roxas, J. L., Ryan, K., Vedantam, G., & Viswanathan, V. K. (2014). Enteropathogenic Escherichia coli dynamically regulates EGFR signaling in intestinal epithelial cells. American journal of physiology. Gastrointestinal and liver physiology, 307(3), G374-80.
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  The diarrheagenic pathogen enteropathogenic Escherichia coli (EPEC) dynamically modulates the survival of infected host intestinal epithelial cells. In the initial stages of infection, several prosurvival signaling events are activated in host cells. These include the phosphorylation of epidermal growth factor receptor (EGFR) and the consequent activation of the phosphatidylinositol-3 kinase/Akt pathway. While studying this pathway in infected epithelial cells, we observed EGFR depletion at later stages of infection, followed subsequently by a decrease in phospho-EGFR. EGFR loss was not dependent on receptor phosphorylation, or on canonical proteasome- and lysosome-dependent processes. Although a type III secretion mutant (ΔescN) stimulated EGFR phosphorylation, it failed to induce receptor degradation. To identify the specific EPEC effector molecule(s) that influenced EGFR stability, epithelial cells infected with isogenic mutant EPEC strains were examined. An EPEC ΔespF strain failed to induce EGFR degradation, whereas EPEC ΔespZ accentuated receptor loss in infected cells. Given the known and contrasting effects of EspF and EspZ on caspase activation, and the known role of proteases in cleaving EGFR, we explored the effect of caspase inhibitors on infection-dependent EGFR loss. The pan-caspase inhibitor Q-VD-OPh blocked EPEC-induced EGFR cleavage in a dose-dependent manner. Taken together, our data suggest that EPEC EspF stimulates caspase-dependent EGFR cleavage and loss, whereas EspZ inhibits this process. Whereas EGFR phosphorylation contributes to the survival of host cells early in infection, EspF-driven caspase activation and consequent EGFR loss likely induce a precipitous increase in host cell death later in the infectious process.
• Merrigan, M. M., Venugopal, A., Roxas, J. L., Anwar, F., Mallozzi, M. J., A., B., Gerding, D. N., Viswanathan, V. K., & Vedantam, G. (2013). Surface-Layer Protein A (SlpA) is a major contributor to host-cell adherence of clostridium difficile. PLoS ONE, 8(11).
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  Abstract: Clostridium difficile is a leading cause of antibiotic-associated diarrhea, and a significant etiologic agent of healthcare-associated infections. The mechanisms of attachment and host colonization of C. difficile are not well defined. We hypothesize that non-toxin bacterial factors, especially those facilitating the interaction of C. difficile with the host gut, contribute to the initiation of C. difficile infection. In this work, we optimized a completely anaerobic, quantitative, epithelial-cell adherence assay for vegetative C. difficile cells, determined adherence proficiency under multiple conditions, and investigated C. difficile surface protein variation via immunological and DNA sequencing approaches focused on Surface-Layer Protein A (SlpA). In total, thirty-six epidemic-associated and non-epidemic associated C. difficile clinical isolates were tested in this study, and displayed intra- and inter-clade differences in attachment that were unrelated to toxin production. SlpA was a major contributor to bacterial adherence, and individual subunits of the protein (varying in sequence between strains) mediated host-cell attachment to different extents. Pre-treatment of host cells with crude or purified SlpA subunits, or incubation of vegetative bacteria with anti-SlpA antisera significantly reduced C. difficile attachment. SlpA-mediated adherence-interference correlated with the attachment efficiency of the strain from which the protein was derived, with maximal blockage observed when SlpA was derived from highly adherent strains. In addition, SlpA-containing preparations from a non-toxigenic strain effectively blocked adherence of a phylogenetically distant, epidemic-associated strain, and vice-versa. Taken together, these results suggest that SlpA plays a major role in C. difficile infection, and that it may represent an attractive target for interventions aimed at abrogating gut colonization by this pathogen.
• Merrigan, M. M., Venugopal, A., Roxas, J. L., Anwar, F., Mallozzi, M. J., Roxas, B. A., Gerding, D. N., Viswanathan, V. K., & Vedantam, G. (2013). Surface-layer protein A (SlpA) is a major contributor to host-cell adherence of Clostridium difficile. PLoS One, 8(11).
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  Clostridium difficile is a leading cause of antibiotic-associated diarrhea, and a significant etiologic agent of healthcare-associated infections. The mechanisms of attachment and host colonization of C. difficile are not well defined. We hypothesize that non-toxin bacterial factors, especially those facilitating the interaction of C. difficile with the host gut, contribute to the initiation of C. difficile infection. In this work, we optimized a completely anaerobic, quantitative, epithelial-cell adherence assay for vegetative C. difficile cells, determined adherence proficiency under multiple conditions, and investigated C. difficile surface protein variation via immunological and DNA sequencing approaches focused on Surface-Layer Protein A (SlpA). In total, thirty-six epidemic-associated and non-epidemic associated C. difficile clinical isolates were tested in this study, and displayed intra- and inter-clade differences in attachment that were unrelated to toxin production. SlpA was a major contributor to bacterial adherence, and individual subunits of the protein (varying in sequence between strains) mediated host-cell attachment to different extents. Pre-treatment of host cells with crude or purified SlpA subunits, or incubation of vegetative bacteria with anti-SlpA antisera significantly reduced C. difficile attachment. SlpA-mediated adherence-interference correlated with the attachment efficiency of the strain from which the protein was derived, with maximal blockage observed when SlpA was derived from highly adherent strains. In addition, SlpA-containing preparations from a non-toxigenic strain effectively blocked adherence of a phylogenetically distant, epidemic-associated strain, and vice-versa. Taken together, these results suggest that SlpA plays a major role in C. difficile infection, and that it may represent an attractive target for interventions aimed at abrogating gut colonization by this pathogen.
• Monteiro, M. A., Ma, Z., Bertolo, L., Jiao, Y., Arroyo, L., Hodgins, D., Mallozzi, M., Vedantam, G., Sagermann, M., Sundsmo, J., & Chow, H. (2013). Carbohydrate-based Clostridium difficile vaccines. Expert Review of Vaccines, 12(4).
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  Clostridium difficile is responsible for thousands of deaths each year and a vaccine would be welcomed, especially one that would disrupt bacterial maintenance, colonization and persistence in carriers and convalescent patients. Structural explorations at the University of Guelph (ON, Canada) discovered that C. difficile may express three phosphorylated polysaccharides, named PSI, PSII and PSIII; this review captures our recent efforts to create vaccines based on these glycans, especially PSII, the common antigen that has precipitated immediate attention. The authors describe the design and immunogenicity of vaccines composed of raw polysaccharides and conjugates thereof. So far, it has been observed that anti-PSII antibodies can be raised in farm animals, mice and hamster models; humans and horses carry anti-PSII IgA and IgG antibodies from natural exposure to C. difficile, respectively; phosphate is an indispensable immunogenic epitope and vaccine-induced PSII antibodies recognize PSII on C. difficile outer surface.
• Monteiro, M. A., Zuchao, M. a., Bertolo, L., Jiao, Y., Arroyo, L., Hodgins, D., Mallozzi, M., Vedantam, G., Sagermann, M., Sundsmo, J., & Chow, H. (2013). Carbohydrate-based Clostridium difficile vaccines. Expert Review of Vaccines, 12(4), 421-431.
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  PMID: 23560922;Abstract: Clostridium difficile is responsible for thousands of deaths each year and a vaccine would be welcomed, especially one that would disrupt bacterial maintenance, colonization and persistence in carriers and convalescent patients. Structural explorations at the University of Guelph (ON, Canada) discovered that C. difficile may express three phosphorylated polysaccharides, named PSI, PSII and PSIII; this review captures our recent efforts to create vaccines based on these glycans, especially PSII, the common antigen that has precipitated immediate attention. The authors describe the design and immunogenicity of vaccines composed of raw polysaccharides and conjugates thereof. So far, it has been observed that anti-PSII antibodies can be raised in farm animals, mice and hamster models; humans and horses carry anti-PSII IgA and IgG antibodies from natural exposure to C. difficile, respectively; phosphate is an indispensable immunogenic epitope and vaccine-induced PSII antibodies recognize PSII on C. difficile outer surface. © 2013 2013 Expert Reviews Ltd.
• Bertolo, L., Boncheff, A. G., Zuchao, M. a., Chen, Y., Wakeford, T., Friendship, R. M., Rosseau, J., Weese, J. S., Chu, M., Mallozzi, M., Vedantam, G., & Monteiro, M. A. (2012). Clostridium difficile carbohydrates: Glucan in spores, PSII common antigen in cells, immunogenicity of PSII in swine and synthesis of a dual C. difficile-ETEC conjugate vaccine. Carbohydrate Research, 354, 79-85.
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  PMID: 22533919;Abstract: Clostridium difficile is responsible for severe diarrhea in humans that may cause death. Spores are the infectious form of C. difficile, which germinate into toxin-producing vegetative cells in response to bile acids. Recently, we discovered that C. difficile cells possess three complex polysaccharides (PSs), named PSI, PSII, and PSIII, in which PSI was only associated with a hypervirulent ribotype 027 strain, PSII was hypothesized to be a common antigen, and PSIII was a water-insoluble polymer. Here, we show that (i) C. difficile spores contain, at least in part, a d-glucan, (ii) PSI is not a ribotype 027-unique antigen, (iii) common antigen PSII may in part be present as a low molecular weight lipoteichoic acid, (iv) selective hydrolysis of PSII yields single PSII repeat units, (v) the glycosyl diester-phosphate linkage affords high flexibility to PSII, and (vi) that PSII is immunogenic in sows. Also, with the intent of creating a dual anti-diarrheal vaccine against C. difficile and enterotoxin Escherichia coli (ETEC) infections in humans, we describe the conjugation of PSII to the ETEC-associated LTB enterotoxin. © 2012 Elsevier Ltd. All rights reserved.
• McQuade, R., Roxas, B., Viswanathan, V. K., & Vedantam, G. (2012). Clostridium difficile clinical isolates exhibit variable susceptibility and proteome alterations upon exposure to mammalian cationic antimicrobial peptides. Anaerobe, 18(6), 614-620.
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  PMID: 23017940;Abstract: Clostridium difficile is a leading cause of hospital-acquired bacterial infections in the United States, and the increased incidence of recurrent C. difficile infections is particularly problematic. The molecular mechanisms of C. difficile colonization, including its ability to evade host innate immune responses, is poorly understood. We hypothesized that epidemic-associated C. difficile clinical isolates would exhibit increased resistance to mammalian, gut-associated, cationic antimicrobial peptides such as the cathelicidin LL-37. Standardized susceptibility tests as well as comparative proteomic analyses revealed that C. difficile strains varied in their responses to LL-37, with epidemic-associated 027 ribotype isolates displaying greater resistance. Further, exposure of C. difficile strains to sub-lethal concentrations of LL-37 resulted in increased resistance to subsequent peptide challenge, suggesting the presence of inducible resistance mechanisms. Correspondingly, LL-37 exposure altered the C. difficile proteome, with marked changes in abundance of cell wall biosynthesis proteins, surface layer proteins, ABC transporters and lysine metabolism pathway components. Taken together, these results suggest that innate immune avoidance mechanisms could facilitate robust colonization by C. difficile. © 2012.
• Roxas, J. L., Wilbur, J. S., Zhang, X., Martinez, G., Vedantam, G., & Viswanathan, V. K. (2012). The enteropathogenic Escherichia coli-secreted protein EspZ inhibits host cell apoptosis. Infection and Immunity, 80(11), 3850-3857.
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  PMID: 22907816;PMCID: PMC3486051;Abstract: The diarrheagenic pathogen enteropathogenic Escherichia coli (EPEC) limits the death of infected enterocytes early in infection. A number of bacterial molecules and host signaling pathways contribute to the enhanced survival of EPEC-infected host cells. EspZ, a type III secreted effector protein that is unique to EPEC and related "attaching and effacing" (A/E) pathogens, plays a role in limiting host cell death, but the precise host signaling pathways responsible for this phenotype are not known. We hypothesized that EspZ contributes to the survival of infected intestinal epithelial cells by interfering with apoptosis. Consistent with previous studies, scanning electron microscopy analysis of intestinal epithelial cells infected with an EPEC espZ mutant ({increment}espZ) showed increased levels of apoptotic and necrotic cells compared to cells infected with the isogenic parent strain. Correspondingly, higher levels of cytosolic cytochrome c and increased activation of caspases 9, 7, and 3 were observed for {increment}espZ strain-infected cells compared to wild-type (WT) EPEC-infected cells. Finally, espZ-transfected epithelial cells were significantly protected from staurosporine-induced, but not tumor necrosis factor alpha (TNF-α)/cycloheximide-induced, apoptosis. Thus, EspZ contributes to epithelial cell survival by mechanisms that include the inhibition of the intrinsic apoptotic pathway. The enhanced survival of infected enterocytes by molecules such as EspZ likely plays a key role in optimal colonization by A/E pathogens. © 2012, American Society for Microbiology.
• Siddiqui, F., O'Connor, J. R., Nagaro, K., Cheknis, A., Sambol, S. P., Vedantam, G., Gerding, D. N., & Johnson, S. (2012). Vaccination with parenteral toxoid B protects hamsters against lethal challenge with toxin A-negative, toxin B-positive clostridium difficile but does not prevent colonization. Journal of Infectious Diseases, 205(1), 128-133.
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  PMID: 22124129;Abstract: Toxin A has historically been regarded as the primary virulence determinant in Clostridium difficile infection, but naturally occurring toxin A-negative, toxin B-positive (A-/B+) C. difficile strains are known to be virulent. To determine the role of toxin B in these strains, we immunized hamsters with a toxoid prepared from purified toxin B to determine whether they would be protected from lethal challenge with an A-/B+ strain of C. difficile. © 2011 The Author.
• Vedantam, G., & Viswanathan, K. (2012). Naming names eponyms and biological history. Gut Microbes, 3(3), 1-3.
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  Abstract: The constraints imposed by available experimental data, and the need for precision, typically limits the eloquence of researchers. Scientists, however, indulge in their literary and poetic selves in the names that they bestow on genes and proteins, on organisms and diseases. We briefly review some familiar names in the Inside Passage, and explore their historical antecedents. © 2012 Landes Bioscience.
• Vedantam, G., & Viswanathan, V. K. (2012). Leptin signaling protects the gut from Entamoeba histolytica infection. Gut Microbes, 3(1).
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  Abstract: The role of the adipose-derived hormone leptin, and leptin receptors, in signaling satiety to the central nervous system and regulating energy balance is well recognized. But leptin also acts on peripheral tissues such as skeletal muscles, adipose tissues, pancreas, liver, intestine and the immune system. The existence of different splice variants of leptin receptor and the numerous intracellular signaling pathways triggered by leptin make this a truly versatile system. Two recent studies explore the link between malnutrition, leptin signaling and susceptibility to amebic infection. These studies point to important and novel aspects of leptin signaling in maintaining gut homeostasis and warding off infections. © 2012 Landes Bioscience.
• Vedantam, G., & Viswanathan, V. K. (2012). Leptin signaling protects the gut from Entamoeba histolytica infection.. Gut microbes, 3(1), 2-3.
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  PMID: 22356851;Abstract: The role of the adipose-derived hormone leptin, and leptin receptors, in signaling satiety to the central nervous system and regulating energy balance is well recognized. But leptin also acts on peripheral tissues such as skeletal muscles, adipose tissues, pancreas, liver, intestine and the immune system. The existence of different splice variants of leptin receptor and the numerous intracellular signaling pathways triggered by leptin make this a truly versatile system. Two recent studies explore the link between malnutrition, leptin signaling and susceptibility to amebic infection. These studies point to important and novel aspects of leptin signaling in maintaining gut homeostasis and warding off infections.
• Vedantam, G., & Viswanathan, V. K. (2012). Naming names: eponyms and biological history.. Gut microbes, 3(3), 173-175.
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  PMID: 22572826;PMCID: PMC3427210;Abstract: The constraints imposed by available experimental data, and the need for precision, typically limits the eloquence of researchers. Scientists, however, indulge in their literary and poetic selves in the names that they bestow on genes and proteins, on organisms and diseases. We briefly review some familiar names in the Inside Passage, and explore their historical antecedents.
• Vedantam, G., & Viswanathan, V. K. (2012). Spirochaetes and their twisted ways. Gut Microbes, 3(5).
• Vedantam, G., & Viswanathan, V. K. (2012). Spirochaetes and their twisted ways.. Gut microbes, 3(5), 399-400.
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  PMID: 22976336;Abstract: Biological systematists have had a long tradition of encountering organisms that are not quite what they seem to be. Among the microbes, horizontal gene transfer and evolutionary pressures result in organisms that have distinguished themselves from their closest relatives. The recent analyses of several Spirochetes reveal members that are not spiral shaped, and ones that appear to have extensively acquired genetic material from phylogenetically distant, but environmentally proximate, organisms.
• Vedantam, G., Clark, A., Chu, M., McQuade, R., Mallozzi, M., & Viswanathan, V. K. (2012). Clostridium difficile infection: Toxins and non-toxin virulence factors, and their contributions to disease establishment and host response. Gut Microbes, 3(2), 121-134.
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  PMID: 22555464;PMCID: PMC3370945;Abstract: Clostridium difficile infection is the leading cause of antibioticand healthcare-associated diarrhea, and its containment and treatment imposes a significant financial burden, estimated to be over $3 billion in the USA alone. Since the year 2000, CDI epidemics/outbreaks have occurred in North America, Europe and Asia. These outbreaks have been variously associated with, or attributed to, the emergence of Clostridium difficile strains with increased virulence, an increase in resistance to commonly used antimicrobials such as the fluoro quinolones, or host susceptibilities, including the use of gastric acid suppressants, to name a few. Efforts to elucidate C. difficile pathogenic mechanisms have been hampered by a lack of molecular tools, manipulatable animal models, and genetic intractability of clinical C. difficile isolates. However, in the past 5 y, painstaking efforts have resulted in the unraveling of multiple C. difficile virulence-associated pathways and mechanisms. We have recently reviewed the disease, its associated risk factors, transmission and interventions (Viswanathan, Gut Microbes 2010). This article summarizes genetics, non-toxin virulence factors, and host-cell biology associated with C. difficile pathogenesis as of 2011, and highlights those findings/factors that may be of interest as future intervention targets. © 2012 Landes Bioscience.
• Vedantam, G., & Tillotson, G. S. (2011). Wrestling with recurrent infections. Scientist, 25(5).
• Vedantam, G., & Viswanathan, V. K. (2011). A more perfect union. Gut Microbes, 2(3).
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  PMID: 21637032;
• Vedantam, G., & Viswanathan, V. K. (2011). Unlocking the gates to inflammatory bowel disease: The role of enterococcus faecalis gelatinase. Gastroenterology, 141(3), 795-798.
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  PMID: 21791208;
• Coursodon, C. F., Trinh, H. T., Mallozzi, M., Vedantam, G., Glock, R. D., & Songer, J. G. (2010). Clostridium perfringens alpha toxin is produced in the intestines of broiler chicks inoculated with an alpha toxin mutant. Anaerobe, 16(6), 614-617.
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  PMID: 20934524;Abstract: Poultry necrotic enteritis (NE) is caused by specific strains of Clostridium perfringens, most of which are type A. The role of alpha toxin (CPA) in NE has been called into question by the finding that an engineered cpa mutant retains full virulence in vivo [9]. This is in contrast to the finding that immunization with CPA toxoids protects against NE. We confirmed the earlier findings, in that 14-day-old Cornish × Rock broiler chicks challenged with a cpa mutant developed lesions compatible with NE in >90% of birds inoculated with the mutant. However, CPA was detected in amounts ranging from 10 to >100 ng per g of gut contents and mucosa in birds inoculated with the cpa mutant, the wildtype strain from which the mutant was constructed, and our positive control strain. There was a direct relationship between lesion severity and amount of CPA detected (R = 0.89-0.99). These findings suggest that the role of CPA in pathogenesis of NE requires further investigation. © 2010 Elsevier Ltd.
• Lepp, D., Roxas, B., Parreira, V. R., Marri, P. R., Rosey, E. L., Gong, J., Songer, J. G., Vedantam, G., & Prescott, J. F. (2010). Identification of novel pathogenicity loci in Clostridium perfringens strains that cause Avian necrotic enteritis. PLoS ONE, 5(5).
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  PMID: 20532244;PMCID: PMC2879425;Abstract: Type A Clostridium perfringens causes poultry necrotic enteritis (NE), an enteric disease of considerable economic importance, yet can also exist as a member of the normal intestinal microbiota. A recently discovered pore-forming toxin, NetB, is associated with pathogenesis in most, but not all, NE isolates. This finding suggested that NE-causing strains may possess other virulence gene(s) not present in commensal type A isolates. We used high-throughput sequencing (HTS) technologies to generate draft genome sequences of seven unrelated C. perfringens poultry NE isolates and one isolate from a healthy bird, and identified additional novel NE-associated genes by comparison with nine publicly available reference genomes. Thirty-one open reading frames (ORFs) were unique to all NE strains and formed the basis for three highly conserved NE-associated loci that we designated NELoc-1 (42 kb), NELoc-2 (11.2 kb) and NELoc-3 (5.6 kb). The largest locus, NELoc-1, consisted of netB and 36 additional genes, including those predicted to encode two leukocidins, an internalin-like protein and a ricin-domain protein. Pulsed-field gel electrophoresis (PFGE) and Southern blotting revealed that the NE strains each carried 2 to 5 large plasmids, and that NELoc-1 and -3 were localized on distinct plasmids of sizes ~85 and ~70 kb, respectively. Sequencing of the regions flanking these loci revealed similarity to previously characterized conjugative plasmids of C. perfringens. These results provide significant insight into the pathogenetic basis of poultry NE and are the first to demonstrate that netB resides in a large, plasmid-encoded locus. Our findings strongly suggest that poultry NE is caused by several novel virulence factors, whose genes are clustered on discrete pathogenicity loci, some of which are plasmid-borne. © 2010 Crown.
• Mallozzi, M., Viswanathan, V. K., & Vedantam, G. (2010). Spore-forming Bacilli and Clostridia in human disease. Future Microbiology, 5(7), 1109-1123.
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  PMID: 20632809;Abstract: Many Gram-positive spore-forming bacteria in the Firmicute phylum are important members of the human commensal microbiota, which, in rare cases, cause opportunistic infections. Other spore-formers, however, have evolved to become dedicated pathogens that can cause a striking variety of diseases. Despite variations in disease presentation, the etiologic agent is often the spore, with bacterially produced toxins playing a central role in the pathophysiology of infection. This review will focus on the specific diseases caused by spores of the Clostridia and Bacilli. © 2010 Future Medicine Ltd.
• Merrigan, M., Venugopal, A., Mallozzi, M., Roxas, B., Viswanathan, V. K., Johnson, S., Gerding, D. N., & Vedantam, G. (2010). Human hypervirulent Clostridium difficile strains exhibit increased sporulation as well as robust toxin production. Journal of Bacteriology, 192(19), 4904-4911.
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  PMID: 20675495;PMCID: PMC2944552;Abstract: Toxigenic Clostridium difficile strains produce two toxins (TcdA and TcdB) during the stationary phase of growth and are the leading cause of antibiotic-associated diarrhea. C. difficile isolates of the molecular type NAP1/027/BI have been associated with severe disease and hospital outbreaks worldwide. It has been suggested that these "hypervirulent" strains produce larger amounts of toxin and that a mutation in a putative negative regulator (TcdC) allows toxin production at all growth phases. To rigorously explore this possibility, we conducted a quantitative examination of the toxin production of multiple hypervirulent and nonhypervirulent C. difficile strains. Toxin gene (tcdA and tcdB) and toxin gene regulator (tcdR and tcdC) expression was also monitored. To obtain additional correlates for the hypervirulence phenotype, sporulation kinetics and efficiency were measured. In the exponential phase, low basal levels of tcdA, tcdB, and tcdR expression were evident in both hypervirulent and nonhypervirulent strains, but contrary to previous assumptions, toxin levels were below the detectable thresholds. While hypervirulent strains displayed robust toxin production during the stationary phase of growth, the amounts were not significantly different from those of the nonhypervirulent strains tested; further, total toxin amounts were directly proportional to tcdA, tcdB, and tcdR gene expression. Interestingly, tcdC expression did not diminish in stationary phase, suggesting that TcdC may have a modulatory rather than a strictly repressive role. Comparative genomic analyses of the closely related nonhypervirulent strains VPI 10463 (the highest toxin producer) and 630 (the lowest toxin producer) revealed polymorphisms in the tcdR ribosome binding site and the tcdR-tcdB intergenic region, suggesting that a mechanistic basis for increased toxin production in VPI 10463 could be increased TcdR translation and read-through transcription of the tcdA and tcdB genes. Hypervirulent isolates produced significantly more spores, and did so earlier, than all other isolates. Increased sporulation, potentially in synergy with robust toxin production, may therefore contribute to the widespread disease now associated with hypervirulent C. difficile strains. Copyright © 2010, American Society for Microbiology. All Rights Reserved.
• Lyras, D., O'Connor, J. R., Howarth, P. M., Sambol, S. P., Carter, G. P., Phumoonna, T., Poon, R., Adams, V., Vedantam, G., Johnson, S., Gerding, D. N., & Rood, J. I. (2009). Toxin B is essential for virulence of Clostridium difficile. Nature, 458(7242), 1176-1179.
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  PMID: 19252482;PMCID: PMC2679968;Abstract: Clostridium difficile is the leading cause of infectious diarrhoea in hospitals worldwide, because of its virulence, spore-forming ability and persistence. C. difficile-associated diseases are induced by antibiotic treatment or disruption of the normal gastrointestinal flora. Recently, morbidity and mortality resulting from C. difficile-associated diseases have increased significantly due to changes in the virulence of the causative strains and antibiotic usage patterns. Since 2002, epidemic toxinotype III NAP1/027 strains, which produce high levels of the major virulence factors, toxin A and toxin B, have emerged. These toxins have 63% amino acid sequence similarity and are members of the large clostridial glucosylating toxin family, which are monoglucosyltransferases that are pro-inflammatory, cytotoxic and enterotoxic in the human colon. Inside host cells, both toxins catalyse the transfer of glucose onto the Rho family of GTPases, leading to cell death. However, the role of these toxins in the context of a C. difficile infection is unknown. Here we describe the construction of isogenic tcdA and tcdB (encoding toxin A and B, respectively) mutants of a virulent C. difficile strain and their use in the hamster disease model to show that toxin B is a key virulence determinant. Previous studies showed that purified toxin A alone can induce most of the pathology observed after infection of hamsters with C. difficile and that toxin B is not toxic in animals unless it is co-administered with toxin A, suggesting that the toxins act synergistically. Our work provides evidence that toxin B, not toxin A, is essential for virulence. Furthermore, it is clear that the importance of these toxins in the context of infection cannot be predicted exclusively from studies using purified toxins, reinforcing the importance of using the natural infection process to dissect the role of toxins in disease. © 2009 Macmillan Publishers Limited.
• Vedantam, G. (2009). Antimicrobial resistance in Bacteroides spp.: Occurrence and dissemination. Future Microbiology, 4(4), 413-423.
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  PMID: 19416011;Abstract: Bacteroides spp. organisms, though important human commensals, are also opportunistic pathogens when they escape the colonic milieu. Resistance to multiple antibiotics has been increasing in Bacteroides spp. for decades, and is primarily due to horizontal gene transfer of a plethora of mobile elements. The mechanistic aspects of conjugation in Bacteroides spp. are only now being elucidated at a functional level. There appear to be key differences between Bacteroides spp. and non-Bacteroides spp. conjugation systems that may contribute to promiscuous gene transfer within and from this genus. This review summarizes the mechanisms of action and resistance of antibiotics used to treat Bacteroides spp. infections, and highlights current information on conjugation-based DNA exchange. © 2009 Future Medicine Ltd.
• Nishiguchi, M. K., Hirsch, A. M., Devinney, R., Vedantam, G., Riley, M. A., & Mansky, L. M. (2008). Deciphering evolutionary mechanisms between mutualistic and pathogenic symbioses. Vie et Milieu, 58(2), 87-106.
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  Abstract: The continuum between mutualistic and pathogenic symbioses has been an underlying theme for understanding the evolution of infection and disease in a number of eukaryotic-microbe associations. The ability to monitor and then predict the spread of infectious diseases may depend upon our knowledge and capabilities of anticipating the behavior of virulent pathogens by studying related, benign symbioses. For instance, the ability of a symbiotic species to infect, colonize, and proliferate efficiently in a susceptible host will depend on a number of factors that influence both partners during the infection. Levels of virulence are not only affected by the genetic and phenotypic composite of the symbiont, but also the life history, mode(s) of transmission, and environmental factors that influence colonization, such as antibiotic treatment. Population dynamics of both host and symbiont, including densities, migration, as well as competition between symbionts will also affect infection rates of the pathogen as well as change the evolutionary dynamics between host and symbiont. It is therefore important to be able to compare the evolution of virulence between a wide range of mutualistic and pathogenic systems in order to determine when and where new infections might occur, and what conditions will render the pathogen ineffective. This perspective focuses on several symbiotic models that compare mutualistic associations to pathogenic forms and the questions posed regarding their evolution and radiation. A common theme among these systems is the prevailing concept of how heritable mutations can eventually lead to novel phenotypes and eventually new species.
• O'Connor, J. R., Galang, M. A., Sambol, S. P., Hecht, D. W., Vedantam, G., Gerding, D. N., & Johnson, S. (2008). Rifampin and rifaximin resistance in clinical isolates of Clostridium difficile. Antimicrobial Agents and Chemotherapy, 52(8), 2813-2817.
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  PMID: 18559647;PMCID: PMC2493101;Abstract: Rifaximin, a poorly absorbed rifamycin derivative, is a promising alternative for the treatment of Clostridium difficile infections. Resistance to this agent has been reported, but no commercial test for rifaximin resistance exists and the molecular basis of this resistance has not been previously studied in C. difficile. To evaluate whether the rifampin Etest would be a suitable substitute for rifaximin susceptibility testing in the clinical setting, we analyzed the in vitro rifaximin susceptibilities of 80 clinical isolates from our collection by agar dilution and compared these results to rifampin susceptibility results obtained by agar dilution and Etest. We found rifaximin susceptibility data to agree with rifampin susceptibility; the MICs of both antimicrobials for all isolates were either very low or very high. Fourteen rifaximin-resistant (MIC, ≥32 μg/ml) unique isolates from patients at diverse locations in three countries were identified. Molecular typing analysis showed that nine (64%) of these isolates belonged to the epidemic BI/NAP1/027 group that is responsible for multiple outbreaks and increased disease severity in the United Kingdom, Europe, and North America. The molecular basis of rifaximin and rifampin resistance in these isolates was investigated by sequence analysis of rpoB, which encodes the β subunit of RNA polymerase, the target of rifamycins. Resistance-associated rpoB sequence differences that resulted in specific amino acid substitutions in an otherwise conserved region of RpoB were found in all resistant isolates. Seven different RpoB amino acid substitutions were identified in the resistant isolates, which were divided into five distinct groups by restriction endonuclease analysis typing. These results suggest that the amino acid substitutions associated with rifamycin resistance were independently derived rather than disseminated from specific rifamycin-resistant clones. We propose that rifaximin resistance in C. difficile results from mutations in RpoB and that rifampin resistance predicts rifaximin resistance for this organism. Copyright © 2008, American Society for Microbiology. All Rights Reserved.
• Hecht, D. W., Kos, I. M., Knopf, S. E., & Vedantam, G. (2007). Characterization of BctA, a mating apparatus protein required for transfer of the Bacteroides fragilis conjugal element BTF-37. Research in Microbiology, 158(7), 600-607.
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  PMID: 17720457;Abstract: We have previously described the identification of BTF-37, an autonomously transferable chromosomal element isolated from Bacteroides fragilis clinical isolate LV23. In this study, we determined that BTF-37 harbors a 16 kb conjugal transfer-encoding region that contains an almost identical copy of a previously identified Bacteroides sp. conjugation-specific gene bctA. BctA has been shown to be required for conjugation in other Bacteroides sp. strains, but no information is available regarding its function. We now report strain distribution and gene expression profiles of bctA. The bctA gene was present in conjugative transposon-harboring B. fragilis strains, but not on a non-transferable B. fragilis plasmid. We also showed that recombinant BctA predominantly localized to the bacterial membrane, and that its N-terminal 32 amino acids were cleaved in an Escherichia coli protein expression system, indicating the presence of a signal sequence. Expression of bctA consistently increased ~3-fold upon pre-exposure of conjugating B. fragilis LV23 to subinhibitory concentrations of tetracycline. Maximum expression occurred 60 min post-tetracycline induction, which also coincided with the time at which highest conjugation frequencies were seen for strain LV23. Based on localization, signal sequence and tetracycline inducibility, our results indicate that BctA is indeed an important member of the Bacteroides conjugal apparatus, since its gene is regulated by conditions that specifically control conjugation. © 2007 Elsevier Masson SAS. All rights reserved.
• Vedantam, G., Knopf, S., & Hecht, D. W. (2006). Bacteroides fragilis mobilizable transposon Tn5520 requires a 71 base pair origin of transfer sequence and a single mobilization protein for relaxosome formation during conjugation. Molecular Microbiology, 59(1), 288-300.
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  PMID: 16359335;Abstract: Tn5520 is the smallest known bacterial mobilizable transposon and was isolated from an antibiotic resistant Bacteroides fragilis clinical isolate. When a conjugation apparatus is provided in trans, Tn5520 is mobilized (transferred) efficiently within, and from, both Bacteroides spp. and Escherichia coli. Only two genes are present on Tn5520; one encodes an integrase, and the other a multifunctional mobilization (Mob) protein BmpH. BmpH is essential for Tn5520 mobility. The focus of this study was to identify the Tn5520 origin of conjugative transfer (oriT) and to study BmpH-oriT binding. We delimited the functional Tn5520 oriT to a 71 bp sequence upstream of the bmpH gene. A plasmid vector harbouring this minimal 71 bp oriT was mobilized at the same frequency as that of intact Tn5520. The minimal oriT contains one 17 bp inverted repeat (IR) sequence. We constructed and tested multiple IR mutants and showed that the IR was essential in its entirety for mobilization. A nick site sequence (5′-GCTAC-3′) was also identified within the minimal oriT; this sequence resembled nick sites found in plasmids of Gram positive origin. We further showed that mutation of a highly conserved GC dinucleotide in the nick site sequence completely abolished mobilization. We also purified BmpH and showed that it specifically bound a Tn5520 oriT fragment in electrophoretic mobility shift assays. We also identified non-nick site sequences within the minimal oriT that were essential for mobilization. We hypothesize that transposon-based single Mob protein systems may contribute to efficient gene dissemination from Bacteroides spp., because fewer DNA processing proteins are required for relaxosome formation. © 2005 Blackwell Publishing Ltd.
• Vedantam, G., & Hecht, D. W. (2003). Antibiotics and anaerobes of gut origin. Current Opinion in Microbiology, 6(5), 457-461.
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  PMID: 14572537;Abstract: Hundreds of bacterial species make up human gut flora. Of these, 99% are anaerobic bacteria. Although anaerobes are part of the normal commensal flora, they can become opportunistic pathogens, causing serious, sometimes fatal infections if they escape from the colonic milieu. Most often, this escape occurs as a result of perforation, surgery, diverticulitis or cancer. Infections involving anaerobic bacteria are often difficult to treat because antibiotic resistance is increasing among the genera, mediated primarily through horizontal transfer of a plethora of mobile DNA transfer factors. Some of these transfer factors can also be transmitted to aerobic bacteria. It is becoming increasingly clear that antibiotic resistance trends have to be carefully monitored, and the transfer factors and mechanisms of transfer understood at a molecular level to avoid negative clinical outcomes when infections involve anaerobic bacteria.
• Vedantam, G., & Hecht, D. W. (2002). Isolation and characterization of BTF-37: Chromosomal DNA captured from Bacteroides fragilis that confers self-transferability and expresses a pilus-like structure in Bacteroides spp. and Escherichia coli. Journal of Bacteriology, 184(3), 728-738.
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  PMID: 11790742;PMCID: PMC139536;Abstract: We report the isolation and preliminary characterization of BTF-37, a new 52-kb transfer factor isolated from Bacteroides fragilis clinical isolate LV23. BTF-37 was obtained by the capture of new DNA in the nonmobilizable Bacteroides-Escherichia coli shuttle vector pGAT400ΔBglII using a functional assay. BTF-37 is self-transferable within and from Bacteroides and also self-transfers in E. coli. Partial DNA sequencing, colony hybridization, and PCR revealed the presence of Tet element-specific sequences in BTF-37. In addition, Tn5520, a small mobilizable transposon that we described previously (G. Vedantam, T. J. Novicki, and D. W. Hecht, J. Bacteriol. 181:2564-2571, 1999), was also coisolated within BTF-37. Scanning and transmission electron microscopy of Tet element-containing Bacteroides spp. and BTF-37-harboring Bacteroides and E. coli strains revealed the presence of pilus-like cell surface structures. These structures were visualized in Bacteroides spp. only when BTF-37 and Tet element strains were induced with subinhibitory concentrations of tetracycline and resembled those encoded by E. coli broad-host-range plasmids. We conclude that we have captured a new, self-transferable transfer factor from B. fragilis LV23 and that this new factor encodes a tetracycline-inducible Bacteroides sp. conjugation apparatus.
• Hecht, D. W., Vedantam, G., & Osmolski, J. R. (2000). Antibiotic resistance among anaerobes: What does it mean?. Anaerobe, 5(3-4), 421-429.
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  Abstract: Antibiotic resistance among anaerobes is increasing, with significant resistance to clindamycin, cephalosporins, cephamycins, and penicillins noted at community hospitals and major medical centers. A total of 615 anaerobes isolated from various Chicago area hospitals in 1996 were tested against 13 antibiotics, and the resistance patterns compared with similar data from 1991. For the Bacteroides fragilis group anaerobes, the most effective antibiotics were the B-lactam/B-lactamase inhibitor combination agents, carbapenems, trovafloxacin and metronidazole. High levels of resistance to clindamycin, piperacillin, cefoxitin and ceftizoxime were seen 1996. For non-B. fragilis group anaerobes, resistance was mush lower, and was notable only in Clostridium spp. (clindamycin and cephamycins) and Prevotella spp. (clindamycin and piperacillin). Despite the prevalence of antibiotic resistance among anaerobes, the frequency of antimicrobial susceptibility testing of anaerobes is declining. There are a number of factors that account for this decline, including a general reduction in funding of hospital clinical laboratories, a concomitant loss of expertise at these institutions, a lack of automated testing for anaerobes, and a failure to consider resistance as important to clinicians. The case for increased susceptibility testing is built upon the changing patterns of resistance such as those reported in this paper, the identification and transfer of genetic determinants corresponding to antibiotic resistance, as well as the correlation of resistance and clinical outcome. (C) 1999 Academic Press.
• Vedantam, G., Novicki, T. J., & Hecht, D. W. (1999). Bacteroides fragilis transfer factor Tn5520: The smallest bacterial mobilizable transposon containing single integrase and mobilization genes that function in Escherichia coli. Journal of Bacteriology, 181(8), 2564-2571.
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  PMID: 10198023;PMCID: PMC93685;Abstract: Many bacterial genera, including Bacteroides spp., harbor mobilizable transposons, a class of transfer factors that carry genes for conjugal DNA transfer and, in some cases, antibiotic resistance. Mobilizable transposons are capable of inserting into and mobilizing other, nontransferable plasmids and are implicated in the dissemination of antibiotic resistance. This paper presents the isolation and characterization of Tn5520, a new mobilizable transposon from Bacteroides fragilis LV23. At 4,692 bp, it is the smallest mobilizable transposon reported from any bacterial genus. Tn5520 was captured from B. fragilis LV23 by using the transfer-deficient shuttle vector pGAT400ΔBgIII. The termini of Tn5520 contain a 22-bp imperfect inverted repeat, and transposition does not result in a target site repeat. Tn5520 also demonstrates insertion site sequence preferences characterized by A-T- rich nucleotide sequences. Tn5520 has been sequenced in its entirety, and two large open reading frames whose predicted protein products exhibit strong sequence similarity to recombinase-integrase enzymes and mobilization proteins, respectively, have been identified. The transfer, mobilization, and transposition properties of Tn5520 have been studied, revealing that Tn5520 mobilizes plasmids in both B. fragilis and Escherichia coli at high frequency and also transposes in E. coli.
• Sitailo, L. A., Zagariya, A. M., Arnold, P. J., Vedantam, G., & Hecht, D. W. (1998). The bacteroides fragilis BtgA mobilization protein binds to the oriT region of pBFTM10. Journal of Bacteriology, 180(18), 4922-4928.
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  PMID: 9733696;PMCID: PMC107518;Abstract: The Bacteroides fragilis conjugal plasmid pBFTM10 contains two genes, btgA and btgB, and a putative oriT region necessary for transfer in Bacteroides fragilis and Escherichia coli. The BtgA protein was predicted to contain a helix-turn-helix motif, indicating possible DNA binding activity. DNA sequence analysis of the region immediately upstream of btgA revealed three sets of inverted repeats, potentially locating the oriT region. A 304- bp DNA fragment comprising this putative oriT region was cloned and confirmed to be the functional pBFTM10 oriT by bacterial conjugation experiments using E. coli and B. fragilis. btgA was cloned and overexpressed in E. coli, and the purified protein was used in electrophoretic mobility shift assays, demonstrating specific binding of BtgA protein to its cognate oriT. DNase I footprint analysis demonstrated that BtgA binds apparently in a single- stranded fashion to the oriT-containing fragment, overlapping inverted repeats I, II, and III and the putative nick site.
• Vedantam, G., & Nichols, B. P. (1998). Characterization of a mutationally altered dihydropteroate synthase contributing to sulfathiazole resistance in Escherichia coli. Microbial Drug Resistance, 4(2), 91-97.
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  PMID: 9650994;Abstract: A series of Escherichia coli strains were selected for increasing resistance to sulfathiazole. Resistance occurred in seven increments, suggesting the accumulation of several mutations that contributed to overall sulfathiazole resistance. All of the resistant strains had a sulfathiazole- resistant dihydropteroate synthase with a Pro to Ser substitution at amino acid position 64. Overproduction of the wild-type enzyme did not result in sulfathiazole resistance, however overproduction of the mutant enzyme resulted in significant resistance. Conversely, overproduction of the wild- type enzyme in a sulfathiazole-resistant background resulted in a decrease in resistance. Although the specific activity of DHPS in crude extracts was not significantly different from the wild type, the amino acid substitution resulted in an enzyme with a tenfold increase in the Km for p-aminobenzoate, and a 100-fold increase in the Ki for sulfathiazole.
• Vedantam, G., Guay, G. G., Austria, N. E., Doktor, S. Z., & Nichols, B. P. (1998). Characterization of mutations contributing to sulfathiazole resistance in Escherichia coli. Antimicrobial Agents and Chemotherapy, 42(1), 88-93.
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  PMID: 9449266;PMCID: PMC105461;Abstract: A sulfathiazole-resistant dihydropteroate synthase (DHPS) present in two different laboratory strains of Escherichia coli repeatedly selected for sulfathiazole resistance was mapped to folP by P1 transduction. The folP mutation in each of the strains was shown to be identical by nucleotide sequence analysis. A single C→T transition resulted in a Pro→Ser substitution at amino acid position 64. Replacement of the mutant folP alleles with wild-type folP significantly reduced the level of resistance to sulfathiazole but did not abolish it, indicating the presence of an additional mutation(s) that contributes to sulfathiazole resistance in the two strains. Transfer of the mutant folP allele to a wild-type background resulted in a strain with only a low level of resistance to sulfathiazole, suggesting that the presence of the resistant DHPS was not in itself sufficient to account for the overall sulfathiazole resistance in these strains of E. coli. Additional characterization of an amplified secondary resistance determinant, sur, present in one of the strains, identified it as the previously identified bicyclomycin resistance determinant bcr, a member of a family of membrane-bound multidrug resistance antiporters. An additional mutation contributing to sulfathiazole resistance, sux, has also been identified and has been shown to affect the histidine response to adenine sensitivity displayed by these purU strains.

Presentations

• Vedantam, G. (2023, April). New Drugs for Old Bugs: Developing Anti-Infectives for C. difficile. Guest Lecture - Research Animal Methods Course.
• Vedantam, G. (2021, May). Clostridioides difficile Infection: An Overview. Ferring Biopharmarceuticals Invited In-Service and Lecture. Virtual: Ferring Biopharmaceuticals.
• Vedantam, G. (2020, December). Women Entrepreneurs of Tucson. Leaders and the Professional Entrepreneurial MindsetThe Innovation Collaboratory.
• Vedantam, G. (2020, June). Coffee With CALS. CALS Development Seminar SeriesCALS Development Office.
• Vedantam, G. (2020, November). Infectious Diseases in Southern Arizona. Physiology Club, University of Arizona.
• Riggs, M. W., Vedantam, G., Campos, S. K., & Viswanathan, V. K. (2018, May). Dissection of the Contributions of Enteropathogenic Escherichia Coli Secreted Effector Protein ESPZ to Virulence. Digestive Diseases Week. Washington DC: American Gastroenterological Association.
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  Invited oral presentation for DDW conference
• Vedantam, G. (2018, November). The power of collaboration: Preventing farm animal and human gut infections using safe and cost-effective biologicals. Ag100 Conference. Phoenix, AZ: Ag100 and UA-CALS.
• Vedantam, G. (2018, November). The role of surface antigens in Clostridioides difficile colonization. Texas A&M University, Department of Microbiology. College Station, TX: Texas A&M University.
• Vedantam, G. (2018, September). Emerging technologies to block gastrointestinal colonization of Clostridium difficile. National Institutes of Health Workshop. Bethesda, MD: National Institute of Allergy and Infectious Diseases.
• Vedantam, G. (2018, September). Gastrointestinal colonization of Clostridium difficile: host and pathogen factors impacting disease. International Clostridium difficile Symposium. Bled, Slovenia: International Clostridium difficile Symposium.
• Vedantam, G., & Viswanathan, V. K. (2018, May). Rho Gtpase Inhibition Contributes to Enteropathogenic Escherichia Coli Esph-Induced Desmosomal Perturbations. Digestive Diseases Week. Washington DC: American Gastroenterological Association.
• Vedantam, G. (2017, August). Non-Toxin Factors Impacting C. difficile Colonization and Virulence. 10th International Clostridial Pathogenesis (ClostPath) Symposium. Ann Arbor, MI: Clostridial Pathogensis Symposium Organizing Committee.
• Vedantam, G. (2017, December). Good Drugs for Bad Bugs: Non-Antibiotic Interventions for C. difficile Infection. Arizona Wellbeing Commons Winter Meeting. Phoenix, AZ: Arizona Wellbeing Commons.
• Vedantam, G. (2017, March). Clostridium difficile Pathogenesis: New Lessons, Old Foe. Lecture invitation. Dept. of Pathobiology, University of Guelph, Guelph, Canada.
• Vedantam, G. (2017, March). Clostridium difficile Pathogenesis. Invited Lecture. Waltham, MA: Ocean Spray Inc..
• Vedantam, G. (2017, May). Clostridium difficile Infection Surveillance: the Good, the Bad and the Ugly. Invited Seminar. St. Mary's Hospital, Tucson, AZ: Association of Professionals in Infection Control and Prevention.
• Vedantam, G. (2017, October). Clostridium difficile Infection Surveillance. Annual National Meeting of the Association of Professionals in Infection Protection. Phoenix, AZ: Association of Professionals in Infection Prevention.
• Vedantam, G. (2017, September). University of Arizona - Contribution to the Arizona Wellbeing Commons. Arizona Wellbeing Commons - VIMID Subgroup. ASU, Phoenix, AZ: Arizona Wellbeing Commons.
• Vedantam, G. -. (2016, April). Clostridium difficile Virulence - it's not all about the Toxins. University of Illinois Dept. of Biological Sciences. Chicago, IL: University of Illinois.
• Vedantam, G. -. (2016, April). Clostridium difficile Virulence Mechanisms. Loyola University Medical Center, Dept. of Microbiology/Immunology. Maywood, IL: Loyola University.
• Vedantam, G. -. (2016, August). Clostridium difficile Virulence - it's not all about the Toxins. University of Illinois College of Mediciane, Dept. of Gastroenterology. Chicago, IL: University of Illinois.
• Vedantam, G. -. (2016, July). Adherence Mechanisms of Clostridium difficile to Gut Epithelial Cells. 13th Biennial Conference of the Anaerobe Society of the Americas. Nashville, TN: Anaerobe Society of the Americas.
• Vedantam, G. -. (2016, June). Clostridium difficile surface biology. General Meeting of the American Society for Microbiology / ICAAC. Boston, MA: American Society for Microbiology.
• Vedantam, G. -. (2016, June). Novel Intervention to Prevent CLostridium difficile Infection. Management Board Meeting, Southern Arizona VA Healthcare System (SAVAHCS). Tucson, AZ: Southern Arizona VA Healthcare System.
• Vedantam, G. -. (2016, May). Clostridium difficile Infection Surveillance in Banner-UMC, Tucson. Infection Control and Banner Administration Meeting. Tucson, AZ.
• Vedantam, G. -. (2016, May). Clostridium difficile Surveillance and Virulence Mechanisms. Invited Seminar at Northern Arizona University. Flagstaff, AZ: Northern Arizona University.
• Vedantam, G. -. (2016, September). Clostridium difficile Infection Surveillance in Tucson-area hospitals. Banner University of Arizona Nursing Grand Rounds. Tucson, AZ.
• Vedantam, G. -. (2014, April). Clostridium difficile infection: New insights into an old pathogen. University of Minnesota, School of Veterinary Medicine Seminar Series. School of Veterinary Medicine, University of Minnesota.
• Vedantam, G. -. (2014, August). Clostridium difficile infection. Dept. of Veterans Affairs Integrated Network Annual Research Forum.
• Vedantam, G. -. (2014, July). Changing skins: How an old pathogen reinvented itself. Minority Health and Health Disparities Intl/ Research Training Forum.
• Vedantam, G. -. (2014, July). Different ways to die: Ribotype 027 C. difficile cell-surface remodeling. Anaerobe Society of the Americas Biennial Conference.
• Vedantam, G. -. (2014, March). Clostridium difficile infection and pathogenesis. Minority Access to Research Careers Forum.
• Vedantam, G. -. (2013, April). Invited Seminar: "Clostridium difficile infection - a One-Health probelm and opportunity". Departmental Seminar Series. University of Arizona.
• Vedantam, G. -. (2013, April). Invited Speaker: "Changing Landscapes: the Clostridium difficile Virulence Spectrum". Health Research Initiative Infectious Diseases Symposium 2013. Ames, Iowa: Iowa State University.
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  Clostridium difficile (CD) is a Gram-positive, spore-forming, anaerobic bacillus that can cause severe gastrointestinal disease. Susceptible populations include elderly humans, and very young non-human mammals such as piglets, calves and foals. C. difficile is also a leading cause of bacterial healthcare-associated infections in the United States, and is responsible for over 400,000 cases of antibiotic-associated diarrhea annually. New, epidemic-associated “hypervirulent” strains of C. difficile (EA-CD) have become prevalent in the past thirteen years; these are associated with increased risk of severe disease, disease recurrence, colectomy and death, as well as hospital persistence and outbreaks. We have performed extensive comparative proteomic analyses on several EA-CD clinical isolates, and found that these strains have significantly altered abundance of cell-surface proteins. Experimental validation of omics results confirms that three functions – cationic antimicrobial peptide resistance, flagellar assembly and capsular polysaccharide display – are substantially altered in EA-CD strains. To facilitate host-signaling and disease establishment studies, we have generated over 40 independent mutations in multiple clinically-relevant C. difficile isolates, as well as tools for controlled expression of C. difficile proteins in vivo. We are using these tools to test our hypothesis that EA-CD strains exhibit a remodeled cell surface, and that this remodeling results in active innate immune avoidance.
• Vedantam, G. -. (2013, August). Invited Seminar: "Virulence characterisitcs of Clostridium difficile clinical isolates". Gastroenterology Grand Rounds, Christian Medical College, India. Vellore, India: Christian Medical College, Vellore, India.
• Vedantam, G. -. (2013, October). Session Chair, Host-Pathogen interactions Session I. International Clostridial Pathogenesis Meeting, Palm Cove, Australia, October 2013.
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  International Meetings on the Molecular Biology and Pathogenesis of Clostridia.The bacterial genus Clostridium is responsible for several extremely important human and veterinary diseases, including tetanus, botulism, gas gangrene, antibiotic-associated diarrhoea, pseudomembranous colitis, human food poisoning, and veterinary enterotoxemias. The ClostPath series of international meetings was instigated in 1995, and is now the leading forum for the international community to meet and discuss progress made in understanding the pathogenic clostridia and their associated diseases.
• Vedantam, G. -. (2013, October). Session Chair, Host-Pathogen interactions Session II. International Clostridial Pathogenesis Meeting, Palm Cove, Australia, October 2013. Palm Cove, Australia, October 2013: International Clostridial Pathogenesis Meeting.
• Vedantam, G. -. (2013, September). Invited Speaker: " Changing skins - how an old pathogen reinvented itself". University of Nevada. Las Vegas, Nevada.: University of Nevada.
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  Invited Seminar
• Vedantam, G. -. (2012). University of Guelph, Ontario, Canada, November 29, 2012. University of Guelph Seminar. Guelph, Canada.
• Vedantam, G. -. (2012). Viropharma Pharmaceuticals, Exton, PA. Viropharma Pharmaceuticals. Exton, PA.
• Vedantam, G. -. (2011). Optimer Pharmaceuticals. Optimer/Cubist Pharmaceuticals. Dallas, Texas.
• Vedantam, G. -. (2013, April). Clostridium difficile Virulence Factors and Intervention Targets. School seminar. Tucson, AZ: SCHOOL OF ANIMAL & COMPARATIVE BIOMEDICAL SCIENCES, Univ. of Arizona.

Poster Presentations

• Mansoor, A., Shehab, K. W., Anwar, F., Viswanathan, V., & Vedantam, G. (2016, July 2016). Active Clostridium difficile Infection Surveillance in a Large Tertiary Medical Center Reveals Significant Strain Variation. Anaerobe Society of the Americas Biennial Meeting. Nashville, TN.
• Vedantam, G., & Viswanathan, V. (2016, July). Clostridium difficile Infection Surveillance in a Tertiary Medical Center Reveals Significant Strain Variations. 13th Biennial Conference of the Anaerobe Society of the Americas. Nashville, TN: Anaerobe Society of the Americas.
• Vedantam, G., & Viswanathan, V. (2016, March). Multiple Student Poster Presentations (6 total). Immunobiology Annual Conference, Bio5, University of Arizona. University of Arizona: Dept. of Immunobiology, University of Arizona.
• Vedantam, G., & Viswanathan, V. (2016, May). Flagellar Glycosylation in CLostridium difficile. American Gastroenterological Association - Digestive Diseases Week. San Diego, CA: American Gastroenterological Association.
• Vedantam, G. (2014, Several). Various POSTER presentations on Clostridium difficile. Various.
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  My students presented posters and talks at multiple venues including:1. UBRP annual conference2. Immunology conference3. ASM regional conference
• Vedantam, G. -. (2013, January). Differential flagellar glycosylation among clinical isolates of Clostridium difficile. 24th Undergraduate Biology Research Symposium, University of Arizona. Tucson, AZ.
• Vedantam, G. -., Anwar, F., Viswanathan, V. -., Mallozzi, M., Wolk, D., Ampel, N., & Noon, A. (2013, April). Characterization of low-toxin producing infections in Southern Arizona hospitals. 53rd Annual Regional Meeting, American Society for Microbiology. Tucson, AZ.
• Vedantam, G. -., Kochanowsky, J., & Mallozzi, M. (2013, November). A novel probiotic to prevent Clostridium difficile colonization and disease. Annual Biomedical Research Conference for Minority Students (ABRCMS). Nashville, TN: NIH.
• Vedantam, G. -., Viswanathan, V. -., Chu, M., Mallozzi, M., & Roxas, B. (2013, April). Analysis of surface polysaccharides in epidemic-associated strains of Clostridium difficile. 53rd Annual Regional Meeting of the American Society for Microbiology. Tucson, AZ.
• Viswanathan, V. K., & Vedantam, G. -. (2013, August,). The EPEC effector EspZ promotes colonization of rabbits and suppresses host cell apoptosis in vivo. FASEB Summer Research Conferences, Gastrintestinal Tract XV. Steamboat Springs, Colorado: Federation of American Society for Experimental Biologists.
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  Other authors:JS Wilbur, Wyatt Byrd, Ed Boedeker
• Viswanathan, V. K., Viswanathan, V. K., Vedantam, G. -., & Vedantam, G. -. (2013, August,). Quantitative global phosphoproteomic analysis of human colonic epithelial cells infected with enteropathogenic E. coli. FASEB Summer Research Conferences, Gastrintestinal Tract XV. Steamboat Springs, Colorado: Federation of American Society for Experimental Biologists.
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  Other authors:Jennifer Roxas, Bryan Roxas, Gayatri Vedantam, Katheryn Ryan, Jessica Franco.