Little information is available on the association and cytological features between bacteria and Malassezia sp in case of canine otitis externa (OE). The aim of this study is to better characterize the association of Malassezia overgrowth in cases of Chronic Otitis Externa (COE) including a bacterial component, either bacterial overgrowth or infection, in dogs (clinical evolution for more than two weeks, bacteria seen on cytology).
Data from 104 ears (64 dogs) with bacterial COE including bacterial identification, OTIS-3 and results of cytology (microbial features and type of associated inflammatory reaction) were analyzed. Kruskal-Wallis rank sum test was performed for statistical analysis.
Malassezia sp were present in 57/104 ears (55%), associated with cocci (17, 30%), mixed population of bacteria (cocci and rods) (37, 65%) and rods (3, 5%). Malassezia were more frequently associated with cocci (p-value = 0,02).
Malassezia sp were positively associated with Staphylococcus sp (39, 70%) but negatively with Pseudomonas aeruginosa (12, 21%) and Streptococcus sp (9, 16%) (p-value = 0,01). Corynebacterium sp and Proteus mirabilis had no influence on Malassezia population in ears.
There was no correlation of OTIS-3 scores and Malassezia population.
Malassezia were associated with bacterial overgrowth (BOG : bacteria adherent to corneocytes) in 46% of cases (26/57), with purulent reaction (neutrophils) in 54% (31/57) and never with pyogranulomatous reaction (PGR : neutrophils + macrophages). There was a negative correlation between Malassezia and PGR (p-value = 0,02). Suppuration was associated with a low number of Malassezia (< 5 Malassezia per HPF) on cytology (26/31 : 84%), compared with BOG (11/26 : 42%) (p-value=8,47.10-10).
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