MSc (Med), Epidemiology and Biostatistics, Faculty of Health Sciences, University of the Witwatersrand / Introduction Given the increasing prevalence of non-typhoidal salmonella in humans, especially as an opportunistic illness associated with HIV, enhanced surveillance for non-typhoidal salmonella (NTS), including screening for antibiotic resistance, is conducted annually in South Africa. We aimed to determine whether there is an association between trimethoprim-sulfamethoxazole (TMP-SMX) prophylaxis and multi-drug resistant NTS infection, to establish whether various factors modify the relationship between TMP-SMX resistance and invasive NTS infection, to examine whether these associations vary by province, and to quantify the resistance rates of NTS to a range of antibiotics. Methods This study was a secondary analysis of enhanced surveillance data on NTS collected between 2003 and 2005. We used descriptive methods to assess the prevalence of NTS by year, province and serotype, and to determine the prevalence of four MDR patterns. Univariate and multivariate regression models were used to investigate the relationships between TMP-SMX prophylaxis and MDR NTS. Univariate logistic regression was used to assess the relationship between invasive NTS and TMP-SMX resistance. Results TMP-SMX prophylaxis is associated with the ACKSSuT pattern (OR 1.91, 95% CI 1.14 – 3.19, p=0.0080) and the AKSSuT MDR pattern (OR 2.00, 95% CI 1.26 – 3.15, p=0.0015). Being on TMP-SMX prophylaxis is associated with an increased odds of having at least one of the four MDR patterns investigated (OR 1.43, 95% CI 1.00 – 2.04, p=0.0388). We also found high rates of resistance to all antibiotics tested except for ciprofloxacin and imipenem. The highest resistance rate was observed for sulfamethoxazole (>75.85%). S. enterica Isangi isolates showed the highest levels of resistance, with 94.43% having at least one MDR pattern. Other factors significantly associated with MDR NTS were ESBL production, prior treatment with antibiotics, HIV status and resistance to TMP-SMX. Discussion and conclusions Isolates from patients on TMP-SMX prophylaxis were associated with an increased odds of having the ACKSSuT and AKSSuT MDR patterns, not taking into account other explanatory factors. These associations did not remain significant when possible confounders were taken into account. Despite the threat of increased multi-drug resistance, TMP-SMX prophylaxis remains important in certain clinical settings.

Salmonella infections remain one of the most common food borne diseases worldwide. Gastroenteritis, which can be caused by many non-typhoidal Salmonella (NTS) serovars, is relatively common in North America. One of the main risk factors of NTS gastroenteritis is travel to endemic areas in the developing world. The current treatment of NTS infections with antibiotics is reserved for severe cases. A growing concern with antibiotic use is that clinical isolates are becoming drug resistant. Although most NTS infections are self-limiting in nature, the burden on the body and recovery can take several months. Thus, it is vital to prevent NTS infections rather than solely rely on treatment. We have previously discovered two novel surface associated polysaccharides in Salmonella: O-Antigen capsule and X-factor. Not only O-Antigen Capsule is considered a common surface antigen, but its’ genes were found to be expressed during in vivo infections in mice. Such an antigen would be a suitable candidate in developing a vaccine against Salmonella induced gastroenteritis. The goal of this research was to evaluate the use of O-Antigen capsule to develop a traveler’s vaccine for NTS associated gastroenteritis. Results and Conclusions: We have developed a purification protocol and purified the capsule and X-factor from Salmonella Typhimurium, Enteritidis, and Heidelberg. Lipopolysaccharide (LPS) was co-isolated with O-Antigen capsule, but removed using Triton extraction. Salmonella LPS is strain-specific and an adaptive immune response against LPS will not provide cross-protection. We generated specific immune sera in rabbits to recognize O-Antigen capsule and X-factor produced by Salmonella Typhimurium and Enteritidis. We used a mouse model to determine the immunization dose of O-Antigen capsule and showed that conjugation is necessary to enhance the immune response in mice. To boost capsule production, we analyzed PyihUTSRQPO activity using a luciferase-based reporter system. Deletion of a putative transcriptional repressor (YihW) resulted in over 100-fold increase in PyihUTSRQPO confirming YihW as a repressor. We have also looked at the effect of growth media, temperature, and sugar precursors on PyihUTSRQPO activity, and were able to show that PyihUTSRQPO has highest activity in Tryptone broth at 30oC in the absence of any additional sugars.

abstract: The emergence of invasive non-Typhoidal Salmonella (iNTS) infections belonging to sequence type (ST) 313 are associated with severe bacteremia and high mortality in sub-Saharan Africa. Distinct features of ST313 strains include resistance to multiple antibiotics, extensive genomic degradation, and atypical clinical diagnosis including bloodstream infections, respiratory symptoms, and fever. Herein, I report the use of dynamic bioreactor technology to profile the impact of physiological fluid shear levels on the pathogenesis-related responses of ST313 pathovar, 5579. I show that culture of 5579 under these conditions induces profoundly different pathogenesis-related phenotypes than those normally observed when cultures are grown conventionally. Surprisingly, in response to physiological fluid shear, 5579 exhibited positive swimming motility, which was unexpected, since this strain was initially thought to be non-motile. Moreover, fluid shear altered the resistance of 5579 to acid, oxidative and bile stress, as well as its ability to colonize human colonic epithelial cells. This work leverages from and advances studies over the past 16 years in the Nickerson lab, which are at the forefront of bacterial mechanosensation and further demonstrates that bacterial pathogens are “hardwired” to respond to the force of fluid shear in ways that are not observed during conventional culture, and stresses the importance of mimicking the dynamic physical force microenvironment when studying host-pathogen interactions. The results from this study lay the foundation for future work to determine the underlying mechanisms operative in 5579 that are responsible for these phenotypic observations. / Dissertation/Thesis / Masters Thesis Biology 2016

Understanding of chronic sequelae development after infection with foodborne pathogens is limited and an increased understanding could assist with the development of more accurate burden of disease estimates. The purpose of this thesis was to determine via systematic review and meta-analysis of the published international literature, the proportion of cases of Salmonella, Campylobacter and E. coli O157 that will develop the chronic sequelae of reactive arthritis, haemolytic uraemic syndrome, irritable bowel syndrome, inflammatory bowel disease or Guillain Barré syndrome. This information can be used to increase our understanding of the relationship between infection and the development of long term health complications while providing a key piece of information for the development of accurate burden of disease estimates. / Canadian Institutes of Health Research Institute of Population and Public Health/Public Health Agency of Canada, Applied Public Health Research Chair (awarded to Jan M. Sargeant)