Effect of a ceruminolytic ear cleaner on clinical, microbiological and ear canal microbiome evolution in canine erythemato-ceruminous otitis externa associated with proliferation of Malassezia yeasts.

Background: Erythemato-ceruminous otitis externa (ECOE) is commonly associated with Malassezia spp. and microbial imbalance.

Hypothesis/objective: To assess the clinical performance of an ear cleaner in dogs suffering from ECOE associated with Malassezia spp. overgrowth and to measure its impact on the microbiota.

Animals: Thirty privately owned dogs suffering from mild-to-moderate ECOE associated with Malassezia spp. overgrowth.

Materials and methods: Pruritus score (PS), clinical score (0-3 Otitis Index Score [OTIS3]: based on secretions, erythema, hyperplasia and ulceration) and cytological score (CS) were assessed on Day (D)0, D7, and D14. Sterile ear swabs were used on D0 and D14 to perform fungal culture DNA extraction, and PCR amplification of the 18 ITS and 16S rRNA gene was carried out to evaluate the composition and changes of the otic microbiome. Ears were cleaned with a cerumenolytic ear cleanser daily, every other day, or twice a week depending on the secretion score.

Results: Fifty-seven ears (30 dogs) completed the study. PS, OTIS-3, and CS were significantly decreased at D7 and D14 (-45%, -43%, -60% and -77%, -66%, -76%, respectively; p < 0.0001 Wilcoxon test). Fungal culture was positive (Malassezia spp.) in only 34 ears at D0 and was negative in all ears at D14. Mycobiota composition was significantly different before and after treatment with an increase of fungal diversity (Shannon index; p < 0.003 Wilcoxon test) at D14 compared to D0. There was no change in bacterial composition.

Conclusions and clinical relevance: In case of ECOE associated with Malassezia spp. overgrowth, the use of the tested ear cleaner showed a positive impact on the fungal dysbiosis and Malassezia spp. overgrowth.