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

One hundred and four strains of Malassezia pachydermatis, 100 isolated from dogs at two geographically separate locations, one from a cat, and 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 fragment polymorphism (RFLP) analysis and Southern blotting against a poly (GT) probe. All but five of the strains shared a common six band karyotype 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 the smallest 800 kbp band was replaced with a double band. Forty-five per 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 RFLP patterns produced by the restriction enzyme HpaII consisted of a limited number of bands which were suitable for visual comparison, although 39 per cent of the strains analysed produced indistinguishable patterns. Southern blots with poly (GT) probe of Bg/II digests showed considerable variation and appeared to provide an ideal method of discriminating between the M. pachydermatis strains.