Obesity is a major predictor for type 2 diabetes. The etiology and comorbidities of these two diseases are associated. Diabetics are twice as likely to contract any type of infection and at greater risk of worse clinical outcomes to infection. However, the individual effects of diet, glycemia and obesity on risk and severity of enteric infection has not been elucidated. Here we show that high blood glucose (i.e. hyperglycemia), independent of obesity, is sufficient to promote mortality during infection with Citrobacter rodentium, a diarrhea-causing pathogen in mice. Mortality was caused by dehydration as a result of excessive Wnt/β-catenin signalling. Our findings highlight the importance of glucose lowering and fluid therapy as opposed to immunological dysfunction, gut barrier defects or bacteraemia as modifiers of outcomes from enteric infection during diabetes. Future work should develop a more comprehensive understanding of the molecular changes that connect hyperglycemia, Wnt/β-catenin pathway and fluid balance during infection. We used the most common model to cause diet-induced obesity in mice to study another enteric pathogen. We showed that long- and short-term high-fat diet (HFD) feeding promoted the colonization and expansion of adherent-invasive Escherichia coli. Higher pathogen burdens in the intestinal tissues and feces were detected in diet-induced obese mice, which coincided with increased distal gut pathology. Initiating the diet one day prior or after infection was sufficient to promote the expansion of adherent-invasive E. coli in the absence of robust weight gain implicating components of diet as a major determinant of pathogen burden. We isolated the dietary factor and found that low fibre content of the high-fat diet was partially responsible for the increased intestinal pathogen burden. Future work should determine how lower fibre alters host and bacterial metabolism in order to promote overgrowth of adherent-invasive E. coli in the gut. / Thesis / Doctor of Philosophy (PhD) / Obesity and diabetes are major public health issues that are connected in many ways, including how diet changes glucose metabolism. Diabetics have a higher risk of contracting infections and also have worse outcomes from infections. It was unknown what factors of obesity or diabetes influence how the immune system combats bacterial infections. The gut is an important site as it is where diet, the immune system, and metabolism all directly interact. We discovered that high blood sugar was associated with death related to dehydration in diabetic, but not necessarily obese mice infected with a diarrhea causing bacteria. Diet-induced obesity in mice infected with bacteria associated with Crohn's disease, showed an overgrowth of bacteria and worse intestinal damage. We isolated the key dietary factor responsible, which was low fibre rather than high fat or sugar. Even one day of lower dietary fibre promoted overgrowth of infectious bacteria in the gut.

<p>Parasite infections around the world are a huge economic burden and decrease the quality of life for many people. Probiotic bacteria are being investigated as a possible treatment for many enteric issues due to their beneficial effects by altering the immune system. Goblet cells are the main source of mucins in the gut, and play an important role in host defense. Alterations in goblet cells and mucin have been implicated in a number of gastrointestinal (GI) diseases and infections. The aim of this study is to develop a probiotic based strategy to modulate goblet cell function in relation to host defense in enteric infection. Utilizing a murine model of parasite infection, <em>Trichuris muris</em>,<em> </em>we examined the effect of daily administration with probiotic <em>Lactobacillus reuteri</em> in different strains of mice and investigation of goblet cell alterations, immune and inflammatory responses in gut, and host defense mechanisms.</p> <p>Treatment with<strong> </strong>live <em>L. reuteri</em> significantly enhanced worm expulsion in resistant C57BL/6 mice and this was associated with significant increase in goblet cells numbers and an increase in IL-10. This lead to investigation of the probiotic effects in IL-10 knock out (KO) and Muc2 KO mice during the infection. There was no difference of worm burden or goblet cell amounts in infected IL-10 KO mice infected treated with probiotic or medium. In infected Muc2 KO mice treated with <em>L. reuteri</em>, there was an earlier increase of goblet cells, and a corresponding decrease in worm numbers. Finally, assessment of this probiotic in susceptible ARK mice revealed no alterations in worm burden, but the treatment prevented the increase in IFN-γ and IL-1β and significantly increased goblet cell numbers.</p> <p>These data demonstrate that altering the flora with probiotic <em>L. reuteri</em> treatment can modulate intestinal goblet cell biology and immune responses in gut, and promote worm expulsion, possibly through an IL-10 mediated mechanism. The increases in goblet cell numbers may also play a role in the early expulsion of the parasite. In addition to enhancing our understanding on the beneficial effect of probiotics in host defense in enteric infection, this research provides new information on gut function in the context of goblet cells and mucins.</p> / Master of Science (MSc)

Typhoid disease, caused by infection with S. Typhi, is a significant cause of mortality and morbidity in resource–poor countries. Efforts have been made to generate a new generation of vaccines that are efficacious and can be given to infants, but have been hindered by a poor understanding of the protective immune response to S. Typhi infection, and in particular by the absence of a correlate of protection. Controlled human infection studies (‘challenge studies’) provide a model for investigating infectious diseases and appraising novel vaccines, including in typhoid disease. This DPhil described the development of a human challenge model of typhoid fever using <en>S. Typhi Quailes strain administered to healthy adults in a sodium bicarbonate buffer. The careful characterisation and manufactured of the strain is described. Following ingestion of 10³ CFU of S. Typhi 55% of participants developed typhoid disease, whilst ingestion of 10⁴ CFU gave a higher attack rate of 65%. At this attack rate vaccine efficacy against human challenge should be demonstrable with a modest sample size. Validity of the model in the appraisal of vaccines was demonstrated using Ty21a, a live, oral, attenuated vaccine. Protective efficacy of Ty21a compared to placebo against challenge was 35%, comparable to that observed in some endemic settings, and the estimated protection in the first year after vaccination in Cochrane meta-analysis. Clinical, microbiological and humoral immune responses were investigated in participants challenged during model development. Typhoid disease was associated with a high fever in most, but not all participants, and a range of symptoms. Severity of disease was variable, and included asymptomatic bacteraemia, as well as fever and symptoms in participants in whom bacteraemia could not be demonstrated. Typhoid disease was associated with a strong humoral immune response to the flagellin and lipopolysaccharide antigens of S. Typhi but not the Vi polysaccharide capsule. Humoral immune responses were not demonstrated in participants without typhoid fever. There was a dose-response relationship to the clinical, microbiological and humoral responses with participants challenged with 10⁴ CFU having more marked responses than those challenged with 10³ CFU. Future success of challenge studies relies on the willing participation of healthy adult volunteers. The motivations for participation, and experiences of participants, were appraised by questionnaire. Whilst financial compensation was an important motivator, it was not the sole motivator. Participants were positive about their experiences, and most would participate again.