2016 ACVIM Forum Research Abstract Program

Twenty-four healthy pet dogs were assigned to one of 3 groups (8 dogs each): control dogs with no intervention (group 1, G1), dogs treated with a soy-based hydrolyzed diet (Purina HA) for 12 weeks with administration of metronidazole 15 mg/kg PO q12 h during weeks 6 to 8 (G2), and dogs maintained on their usual diet and administered the same dose of metronidazole for 2 weeks (G3). Feces and blood were collected at day (D) 0, 21 and 42 in G1; and D0, 14, 28 and 42 days in G2 and G3. Microbial communities were analyzed by Illumina sequencing of 16S rRNA genes, and the software PICRUSt was used to predict functional gene families. The serum and fecal metabolome was assessed by an untargeted approach combining various mass spectrometry platforms. All assessed parameters were adjusted for multiple comparisons using the Benjamin Hochberg adjustment, and an adjusted P < 0.05 was considered significant. No significant differences in any of the evaluated parameters were observed in G1 (control group). Also, in G2, the dietary switch to the hydrolyzed diet (between baseline and week 6) did not lead to any significant changes in any of the evaluated parameters. However, when dogs in G2 and the dogs in G3 received metronidazole, significant changes were observed. Because the responses in these 2 groups were similar, they were combined for statistical analysis. Microbiome structure and diversity were significantly altered between baseline and time of completion of metronidazole treatment, and also 4 weeks after end of metronidazole treatment (ANOSIM: P = 0.002). The most significant changes were increases in E. coli and decreases in Firmicutes. Functional gene families found to be significantly more abundant during antibiotic administration included: lipopolysaccharide biosynthesis, glutathione metabolism, recombination and repair proteins, tryptophan metabolism, and fatty acid metabolism (P < 0.0001 for all). At cessation of antibiotic administration (D14), functional gene families found to be significantly more abundant included: bile secretion, xylene degradation, dioxin degradation, and signal transduction mechanisms (P < 0.0001 for all). Metronidazole lead to alteration in 98 out of 469 measured fecal metabolites. Major changes observed were reduction in secondary bile acids (P < 0.001), increases in oxidative stress pathways (P < 0.0001), and changes in tryptophan-indole pathways (P < 0.001). While most of the changes were reversed 14 days after the end of antibiotic administration, some of the evaluated bacterial taxa and metabolites remained significantly altered up to 4 weeks after end of administration (end of study).