Effects of High-Dose Prednisone on the Gastrointestinal Microbiota of Healthy Dogs

The effects of high-dose glucocorticoids on the gastrointestinal microbiota of healthy dogs are unknown. This study's aim was to investigate the effects of immunosuppressive doses of prednisone on the fecal microbiota and the gastric and duodenal mucosal microbiota in healthy dogs. Twelve healthy adult dogs were enrolled into a randomized, double-blinded, placebo-controlled trial. Dogs were evaluated on days 0, 14, and 28 following treatments with either prednisone (2 mg/kg/d) or placebo. Outcome measures included (1) composition and abundance of the fecal microbiota (via high-throughput sequencing of the 16S rRNA gene and qPCR-based dysbiosis index [DI]) and (2) spatial distribution of the gastric and duodenal mucosal microbiota using fluorescence in situ hybridization (FISH). No significant difference in alpha and beta diversity or amplicon sequence variants of the fecal microbiota was observed between treatment groups. Blautia spp. concentrations via qPCR were significantly decreased between prednisone group timepoints 2 and 3. Compared to placebo group dogs, prednisone group dogs showed significantly increased gastric mucosal helicobacters and increased mucosal-associated total bacteria and Bacteroides in duodenal biopsies over the treatment period. The results indicate that immunosuppressive dosages of prednisone alter the mucosal microbiota of healthy dogs in a time-dependent manner, which may disrupt mucosal homeostasis. This report is significant, since it addresses a knowledge gap in our understanding of the effects of glucocorticoids on the gastrointestinal mucosal microbiota of healthy dogs.