Ear canal microbiota – a comparison between healthy dogs and atopic dogs without clinical signs of otitis externa

BACKGROUND: The canine skin microbiota has been evaluated using relatively new microbiological techniques; studies have shown a difference in the composition of bacterial populations between healthy dogs and those with canine atopic dermatitis (cAD). However, little has been reported concerning the ear canal microbiota despite the fact that otitis externa is a common problem in dogs with cAD. HYPOTHESIS/OBJECTIVES: The study evaluated the ear canal microbiota of healthy dogs and atopic dogs without clinical signs of otitis. ANIMALS: Nine healthy privately owned dogs and 11 dogs with a diagnosis of cAD. METHODS AND MATERIALS: Ear swabs from the two groups were used for global bacterial DNA extraction. V1-V3 hypervariable 16S rDNA amplicon libraries were prepared for each sample and sequenced with MiSeq Illumina sequence (V3 kit). Taxonomical assignment and clustering were performed with Mothur using SILVA database. RESULTS: The ear canal microbiota showed changes in diversity similar to those reported for canine skin and seemed to be stable during the period of the study (28 days). Evidence of dysbiosis was observed in the atopic dogs, with increased abundance of Staphylococcus spp. and Ralstonia spp. (P < 0.05). Escherichia spp. also were found to be more abundant in healthy dogs. CONCLUSIONS AND CLINICAL IMPORTANCE: This study demonstrated a shift in bacterial populations between allergic and healthy dogs. The observed results in the ear canal are similar to those reported on the skin and could explain the propensity of allergic dogs to develop bacterial otitis.