Characterization of markedly lipid-dependent Malassezia pachydermatis isolates from healthy dogs

When 244 Malassezia colonies which had been isolated from a colony of Beagle dogs using modified Dixon's agar were sub-cultured on Sabouraud's dextrose agar to determine their lipid dependence, 30 showed poor growth resembling M. furfur, whereas the remainder were typical of M. pachydermatis. Eight of the 10 poor growing isolates selected for further study formed colonies typical of M. pachydermatis after five passages on Sabouraud's dextrose agar at 4 d intervals and two continued to show poor growth. Nine isolates had enzyme profiles identical to those of typical M. pachydermatis isolates, and one resembled M. furfur. However, seven of the poor growing isolates which were karyotyped had patterns typical of M. pachydermatis. Poor growing isolates and their non-lipid-dependent 'revertants' had identical restriction fragment length polymorphism patterns and poly(GT) hybridization profiles. These observations show that some M. pachydermatis isolates grow poorly when sub-cultured onto Sabouraud's dextrose agar and may be incorrectly identified as M. furfur if further studies are not performed.