The intestinal microbiota is increasingly linked to the pathogenesis of idiopathic inflammatory bowel disease (IBD) in dogs. Similar to IBD in humans, microbial imbalances in dogs are characterized by a decrease in diversity and altered concentrations of beneficial/harmful species. While studies have reported alterations in fecal (luminal) bacterial populations, only limited information is available about the mucosal microbiota of IBD at diagnosis and in response to medical therapy. The aim of the present study was to characterize the mucosa-associated microbiota and determine the clinical, microbiological, and mucosal homeostatic effects of probiotic therapy in CIBD.Methods:
A prospective, randomized double-blind clinical trial was performed. Thirty-four dogs diagnosed with moderate-to-severe IBD (CIBDAI score >5) were randomized to receive standard therapy (i.e., elimination diet and oral glucocorticoids = ST) with or without a multi-strain probiotic*. The mucosal microbiota from endoscopic intestinal biopsies of IBD dogs was evaluated by fluorescence in situ hybridization (FISH) and qPCR targeting the 16S rRNA genes of total bacteria, group-specific organisms, and individual bacterial species shown to be relevant in human and canine IBD. Epithelial tight junction protein (TJP) expression was studied using immunohistochemistry. Clinical signs and changes in mucosal microbiota and TJP expression were temporally assessed before and after 8 weeks of probiotic therapy.Results:
Both dog groups showed a reduction in GI signs after 8 weeks of IBD therapy compared to baseline CIBDAI scores (P < 0.05). ST and probiotic therapy modulated the number of total bacteria of IBD dogs in a similar fashion. Changes in mucosal bacteria mirrored those for total bacteria except that Eub338-positive bacteria failed to increase (P = 0.13) in dogs treated with probiotic. When evaluating changes in the spatial distribution of mucosal bacteria following therapy, significant increases in bacteria hybridizing to probes against Eubacteria, Bifidobacterium spp., Fecalibacterium spp., and Enterobacteriaceae were observed within adherent mucus of dogs treated with ST. These same bacterial groups and Lactobacillus spp. were increased within the adherent mucus of IBD dogs receiving probiotic (P < 0.001). A comparison of treatment effects affecting adherent mucus bacteria showed that ST therapy preferentially increased Bifidobacteria spp. (P < 0.05) while probiotic therapy preferentially increased Lactobacillus spp. (P < 0.001). Probiotic therapy was associated with up-regulated (P < 0.05) expression of TJPs E-cadherin, occludin, and zonulin versus ST. Quantitative PCR failed to reveal significant shifts in fecal microbial composition regardless of treatment.Conclusions:
This is the first study utilizing FISH methods to localize, quantify, and directly compare different medical treatments on mucosal bacterial populations in CIBD. The most important finding of this study obtained using FISH was the absence of a significant difference in mucosal bacteria following treatment of IBD dogs with ST versus probiotic. Microbiota from mucosal samples more clearly represent the underlying microbial dysbiosis, at diagnosis and in response to treatment, as compared to fecal samples. *Visbiome which contains the same strains, in the same concentration and proportions, and is therapeutically equivalent to the VSL#3 brand probiotic blend as produced before January 31, 2016.