An association between mucosa-adherent commensal bacteria and inflammatory bowel disease (IBD) has been proposed for humans. There are no reports characterizing the mucosa-adherent duodenal microbiota in dogs with idiopathic IBD using molecular methods. The aim of this study was to investigate differences in the mucosa-adherent duodenal microbiota between dogs with idiopathic IBD and healthy dogs. Duodenal biopsy samples were collected from seven dogs with IBD and seven healthy control dogs. DNA was extracted, 16S ribosomal RNA genes were amplified and 16S rRNA gene clone libraries were constructed and compared between groups. A total of 1035 clones were selected, and based on a 98% similarity criterion, 133 unique phylotypes were identified across all dogs. These phylotypes belonged to seven bacterial phyla: Proteobacteria (52.9%), Firmicutes (26.1%), Bacteroidetes (7.7%), Actinobacteria (8.6%), Fusobacteria (4.4%), Tenericutes (0.2%) and Verrucomicrobia (0.1%). Significant differences were identified in the relative abundance of several bacterial groups between dogs with IBD and healthy dogs (p<0.001). Healthy dogs and dogs with IBD clustered according to their disease status. Dogs with IBD had a significantly higher abundance of clones belonging to Alpha-, Beta-, and Gamma-proteobacteria (p<0.0001 for all classes), and a significantly lower abundance of Clostridia (p<0.0001). Bacteria of the genera Pseudomonas, Acinetobacter, Conchiformibious, Achromobacter, Brucella, and Brevundimonas, were significantly more abundant in dogs with IBD. In conclusion, significant differences of the mucosa-adherent duodenal microbiota were observed between dogs with idiopathic IBD and healthy dogs in this study. These results warrant further investigations into the role of the intestinal microbiota in the pathophysiology of canine IBD.
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