CHARACTERISTICS OF MALASSEZIA-PACHYDERMATIS STRAINS ISOLATED FROM CANINE OTITIS-EXTERNA

The morphological, cultural and biochemical characteristics of 80 M. p achydermatis strains isolated from cases of canine otitis externa were studied. Microscopically, the strains could be subdivided into two ph enotypes. All M. pachydermatis strains grew well on Sabouraud glucose, yeast morphology and modified malt extract agar, but formed two disti nct colony types. All strains were characterized by no fermentation. A ssimilation of glucose, mannitol (42 strains), sorbitol (40 strains) a nd peptone was observed, but no ethanol assimilation. Urease and catal ase tests were positive, while indole and acetoin production was not d etected. All strains showed proteinase, caseinase, lecithinase and per oxidase positivity but to varying extents. Esterase activity was obser ved for all Malassezia strains when using Tween 20, 40 and 60, whereas Tween 80 was hydrolysed by only 42 strains. No coagulase or haemagglu tinating activities were detected. When compared for satellite phenome non and vitamin requirements, some Malassezia strains could not grow i n the absence of nicotinic acid but grew well in the presence of staph ylococci. In susceptibility tests, all strains showed the highest susc eptibility to ketoconazole. On the basis of the biochemical difference s, M. pachydermatis seems to be a heterogeneous species and can be div ided into two groups.