APPLICATION OF DNA TYPING METHODS TO THE STUDY OF THE EPIDEMIOLOGY OFMALASSEZIA-PACHYDERMATIS

One hundred and four strains of Malassezia pachydermatis, 100 isolated from dogs at two geographically separate locations, one from a cat, a nd three from young bears, have been karyotyped. Cellular nucleic acid has been extracted from a selection of these strains, assayed for the presence of extrachromosomal nucleic acid, studied by restriction fra gment polymorphism (RFLP) analysis and Southern blotting against a pol y (GT) probe. All but five of the strains shared a common six band kar yotype pattern with the bands estimated to be, 800 kbp, 1250 kbp, 1450 kbp, 1500 kbp, 1850 kbp and 1900 kbp. In the remaining five strains t he smallest 800 kbp band was replaced with a double band. Forty-five p er cent of the isolates tested carried a 6.4 kbp RNA 'plasmid' and 21 per cent of the isolates also carried a 1.8 kbp RNA 'plasmid'. The RFL P patterns produced by the restriction enzyme HpaII consisted of a lim ited number of bands which were suitable for visual comparison, althou gh 39 per cent of the strains analysed produced indistinguishable patt erns. Southern blots with poly (GT) probe of Bg/II digests showed cons iderable variation and appeared to provide an ideal method of discrimi nating between the M. pachydermatis strains.