Exploring Early Life Microbial Interventions and Subsequent Disease Resistance in a Swine-derived Bacterial Gnotobiotic Mouse Model
Creators: Lantz, Hannah L
Publisher: name: University of Alberta Library
Year: 2022

<p>Many associations between the gut microbiota, host health, and disease have been revealed, however, mechanistic research to determine causality is necessary. Gnotobiotic animal models, where all organisms are known, are the gold standard to examine mechanisms of causality and gnotobiotic mice are the most widely implemented animal model. The overall objective of this thesis was to create a novel gnotobiotic mouse model colonized with a swine defined community (DC) to study the effects of early life Escherichia coli and amoxicillin administration on subsequent Salmonella resistance previously investigated in conventional pigs. To create a DC, a swine-derived bacterial culture collection with 35 species spanning 15 genera, 12 families, and 6 phyla was generated. The curation of a representative pig DC with whole genomes consisting of 16 species was established based on the proposed swine core microbiota and prominent bacteria in pre-weaning piglets. Germ-free C57BL/6J male mice (N = 8) were colonized with the pig DC to determine the colonization ability and pattern in a mouse model. The majority (14/16 species) of the DC colonized the mouse gut except for Prevotella copri and Streptococcus hyointestinalis. The β diversity in the ileum significantly differed from the cecum, colon, and feces, which was driven by the enrichment of Streptococcus and Lactobacillus in the ileum versus Bacteroides in the lower tract; and the total bacteria load in the ileum was significantly lower than the other regions (P &lt; 0.05). Similar biogeographical colonization and bacterial loads are observed in pigs. Preliminary results suggesting that E. coli and amoxicillin administration in early life can enhance piglets’ immune responsiveness to intraperitoneal heat-killed Salmonella enterica serovar Typhimurium (S. Tm) were tested in our swine DC mouse model. Female C57BL/6J mice colonized with the swine DC with or without E. coli were bred and during the first two weeks of their pups’ lives, dams were either administered sterile amoxicillin drinking water or sterile drinking water. The four pup treatment groups (E. coli + Amoxicillin, n = 5; E. coli, n = 8; Amoxicillin, n = 8; and Control, n = 8) were then challenged with live S. Tm SL1344 at six weeks of age, after normalization of the gut microbiota on post-natal day 21. The S. Tm load in both the ileum and liver significantly differed by treatment, with the lowest loads observed in the EA group, suggesting that the combined neonatal exposure to E. coli and amoxicillin does facilitate local and systemic pathogen burden later in life (P &lt; 0.05). At 48 hrs post-infection, there were no differences in inflammatory cytokine levels between treatments. Furthermore, sex differences in S. Tm load and cytokine production were observed without accompanying microbiota differences. Males suffered from significantly greater S. Tm loads in the ileum, cecum, and liver with significantly increased IL-6 and IL-10 (P &lt; 0.05). While largely underexplored in S. Tm infection, sexual dimorphism was consistent with other enteric infections and may be due to a greater innate and cell-mediated immune response without excessive proinflammatory cytokine production. While these results show that early life microbial and antibiotic interventions have long lasting impacts on S. Tm resistance, further research is needed to unravel the mechanisms behind early life E. coli and amoxicillin exposure on immune system development and subsequent disease resistance.</p>