In vivo amoxicillin treatment followed by in vitro salmonella challenge

Salmonella enterica serovar Typhimurium is an animal welfare and public health concern due to its ability to parasite livestock and potentially contaminate meat products. In pigs, it is associated with enterocolitis and diarrhea, whereas some individuals may become life-long carriers. To reduce Salmonella shedding and the risk of pork contamination, antibiotic therapy is used and can contribute to antimicrobial resistance. Here we hypothesized that immune system education by the microbiota can play a role in intestinal resilience to infection. We used amoxicillin (15mg/Kg) to modulate the intestinal microbiome of 10 piglets, paired with same age pigs that received a placebo (n=10) from 0 to 14 days of age. Animals were euthanized when 4-weeks old. Each pig donated colon sections for ex vivo culture (n=20 explants/pig). Explants were inoculated with S. Typhimurium, PBS or LPS. The gut bacteriome was characterized by sequencing of the 16S rRNA at 7, 21 days of age, and upon in vitro culture. In vivo antibiotic treatment led to ?-diversity differences between groups at all times (P<0.05), while ?-diversity did not differ between amoxicillin and placebo groups on day 21 and at euthanasia (P<0.03 on day 7). Explant microbiomes were not different from in vivo. No significant differences in epithelial cell necrosis scores were observed between amoxicillin and placebo groups after exposure to Salmonella, even though median scores were lower in the amoxicillin group. Both groups did have significantly higher necrosis scores than the PBS group (P<0.05). Activation of immune-related cascades in control explants from the amoxicillin group was observed, whereas Salmonella exposure activated specific cellular repair, wound healing and macrophage pathogen inhibition pathways that were significantly different from placebo pigs. These suggest that immune education by the microbiota may be developed as a tool to mitigate intestinal lesions following pathogen exposure.