The otic microbiota and mycobiota in a referral population of dogs in eastern USA with otitis externa

Abstract

Background -Canine otitis externa (OE) is a common inflammatory disease that is frequently complicated by secondary bacterial and/or yeast infections. The otic microbial population is more complex than appreciated by cytological methods and aerobic culture alone.Hypothesis/objectives -Differences in bacterial and fungal populations of the external ear canal will correlate with specific cytological and culture-based definitions of bacterial and Malassezia otitis.Animals -Forty client-owned dogs; 30 with OE and 10 with healthy ears.Methods and materials -Prospective study comparing cytological samples, aerobic bacterial cultures and culture-independent sequencing-based analyses of the external ear canal. Subjects with OE included 10 dogs with only cocci [≥25/high power field (HPF)] on cytological evaluation and culture of Staphylococcus spp.; 10 dogs with rods (≥25/HPF) and exclusive culture of Pseudomonas aeruginosa; 10 dogs with only yeast on cytological results morphologically compatible with Malassezia spp. (≥5/HPF).Results -Staphylococcus was the most abundant taxa across all groups. Ears cytologically positive for cocci had decreased diversity, and all types of OE were associated with decreased fungal diversity compared to controls.Conclusions and clinical importance -Cytological and culture-based assessment of the ear canal is not predictive of the diverse microbiota of the ear canal in cases of Pseudomonas or Malassezia otitis. Less abundant bacterial taxa in cases of staphylococcal OE are worth scrutiny for future biological therapy.

Cerumen microbial community shifts between healthy and otitis affected dogs

“…Regarding microbiota in dogs with otitis, our results are consistent with those of previous reports [7,10,19,21], showing a reduced bacterial richness in otitis affected dogs. Indeed, in the otitis affected group, we found 18 phyla and a total of 316 genera vs. the 19 phyla and 391 genera detected in healthy animals.…”

“…The microbial diversity found in the ear canal in this study is consistent with other previous findings based on 16S rRNA amplicon sequencing [7,12,15,[19][20][21]. The application of high throughput sequencing methods to ear microbiota analysis evidenced that the ear bacterial community in dogs is much more complex than known in the past based on culture-dependent methods [7,12,15,[19][20][21]. Our results showed the presence of bacteria belonging to 19 different Phyla in healthy dogs, a value that is consistent with those reported in previous studies PLOS ONE [19,20].…”

“…has been elsewhere found at lower frequencies in healthy animals [20]. Anyway this bacterial genus includes ubiquitous bacteria often found on the skin and ear microbiota of animals and humans [19][20][21]43], and this evidence might support the hypothesis that dysbiosis or use of antibiotics can select the flora to a purulent otitis with multi resistant Pseudomonas. Moreover, at the genus level, the microbiota of most affected animals appeared to be characterized by high relative abundance (>10%) of a single bacterial genus, either alone or in combination with another one.…”

“…While the presence of Staphylococcus spp. has been widely demonstrated in the ear microbiota of healthy dogs [19][20][21], Pseudomonas spp. has been elsewhere found at lower frequencies in healthy animals [20].…”

“…Decreased bacterial richness and diversity have been found in dogs with otits externa, with a severe increase of Staphylococcus spp. [20,21], whereas a very recent study demontrated a correlation between bacterial and fungal populations of the external ear canal and otitis caused by Pseudomonas and Malassezia [21]. Malassezia pachydermatis has been reported as the dominant fungi in the ear skin of healthy dogs, while dogs with clinical otitis exhibited an overgrowth of M. globosa and M. sympodialis [22].…”