Bacterial microbiota and proinflammatory cytokines in the anal sacs of treated and untreated atopic dogs: Comparison with a healthy control group

Abstract

The pathogenesis of anal sacculitis has not been extensively investigated, although atopic dogs seem to be predisposed to the disease. The aim of this study was therefore to characterize and compare the bacterial microbiota and pro-inflammatory cytokines in the anal sacs of dogs from three groups (healthy dogs, untreated atopic dogs and atopic dogs receiving antipruritic treatment or allergen-specific immunotherapy) in order to determine whether changes could be at the origin of anal sacculitis in atopic dogs. Bacterial populations of anal sac secretions from fifteen healthy dogs, fourteen untreated and six treated atopic dogs were characterized by sequencing the V4 region of the 16S rRNA gene using Illumina technology. Proinflammatory cytokines were analyzed with the Luminex multiplex test. Community membership and structure were significantly different between the anal sacs of healthy and untreated atopic dogs (P = 0.002 and P = 0.003, respectively) and between those of untreated and treated atopic dogs (P = 0.012 and P = 0.017, respectively). However, the community structure was similar in healthy and treated atopic dogs (P = 0.332). Among the proinflammatory cytokines assessed, there was no significant difference between groups, except for interleukin 8 which was higher in the anal sacs of untreated atopic dogs compared to treated atopic dogs (P = 0.02), and tumor necrosis factor-alpha which was lower in the anal sacs of healthy dogs compared to treated atopic dogs (P = 0.04). These results reveal a dysbiosis in the anal sacs of atopic dogs, which may partially explain the predisposition of atopic dogs to develop bacterial anal sacculitis. Treatments received by atopic dogs (oclacitinib, desloratadine and allergen-specific immunotherapy) shift the microbiota of the anal sacs towards that of healthy dogs. Further studies are required to identify significant cytokines contributing to anal sacculitis in atopic dogs.

Fig 1. Mean relative abundance of the main bacterial genera (>1%) found in the anal sacs and rectum of healthy dogs and atopic dogs (untreated and treated).

AS_CON, Anal sacs of healthy dogs; AS_UAD, Anal sacs of untreated atopic dogs; AS_TAD, Anal sacs of treated atopic dogs; REC_CON, Rectum of healthy dogs; REC_UAD, Rectum of untreated atopic dogs; REC_TAD, Rectum of treated atopic dogs.

Fig 2. Linear discriminant analysis (LDA) effect size (LEfSe) indicating genera whose abundance is significantly different between the rectal microbiota in healthy dogs and atopic dogs (untreated and treated).

REC_CON, Rectum of healthy dogs; REC_UAD, Rectum of untreated atopic dogs; REC_TAD, Rectum of treated atopic dogs.

Fig 3. Alpha diversity measurements in different sites (anal sacs and rectum) in healthy dogs, untreated AD, and treated AD.

A–number of genera observed. B–Chao index. C–Simpson index. D–Shannon index. * P < 0.001. ** P = 0.012. A P value lower than 0.05 was considered statistically significant. AS_CON, Anal sacs of healthy dogs, AS_UAD, Anal sacs of untreated atopic dogs; AS_TAD, Anal sacs of treated atopic dogs; REC_CON, Rectum of healthy dogs; REC_UAD, Rectum of untreated atopic dogs; REC_TAD, Rectum of treated atopic dogs.

Fig 4

Principal Coordinate Analysis plots of the community membership comparing the anal sacs microbiota of healthy dogs, untreated AD, and treated AD (A) and the rectum microbiota of healthy dogs, untreated AD, and treated AD (B). AS_CON, Anal sacs of healthy dogs; AS_UAD, Anal sacs of untreated atopic dogs; AS_TAD, Anal sacs of treated atopic dogs; REC_CON, Rectum of healthy dogs; REC_UAD, Rectum of untreated atopic dogs; REC_TAD, Rectum of treated atopic dogs.

Fig 5

Principal Coordinate Analysis plots of the community structure comparing the anal sacs microbiota of healthy dogs with that of untreated and treated atopic dogs (A) and the rectum microbiota of healthy dogs with that of untreated and treated atopic dogs (B). AS_CON, Anal sacs of healthy dogs; AS_UAD, Anal sacs of untreated atopic dogs; AS_TAD, Anal sacs of treated atopic dogs; REC_CON, Rectum of healthy dogs; REC_UAD, Rectum of untreated atopic dogs; REC_TAD, Rectum of treated atopic dogs.