Malassezia globosa as the causative agent of pityriasis versicolor

The taxonomic revision carried out in 1996 on the genus Malassezia, which now comprises seven different species, made necessary a re-evaluation of the data concerning the ecology and pathogenicity of these lipophilic yeasts. Very little has been published since then.

The aim of this work was to contribute to the knowledge of the aetiology of pityriasis versicolor (PV) with a mycological study made according to the new species.

Ninety-six patients with PV completed the study. In all of them, samples were taken from the lesions for direct microscopy with KOH+ Parker ink and culture. Samples were also taken from normal skin of the trunk and the forehead of the same patients for culture. Cultures were made in modified Dixon medium in Petri dishes, incubated at 31 degrees C and the isolates were identified by morphological and physiological characteristics.

In the PV lesions, direct microscopy always showed the typical mixture of globose blastoconidia and pseudomycelium. Only one patient, having received previous topical antimycotic treatment, was negative. The spherical yeasts observed in vivo were morphologically identical to the globose yeasts characteristic of M. globosa. In culture, M. globosa was found in 97% of cases, alone in 60% of them and associated with M. sympodialis in 29% and M. slooffiae in 7%. These two species were also found in similar percentages on the clinically uninvolved skin of the trunk, whereas M. globosa was not isolated at these sites. However, on the forehead, a small number of colonies of M. globosa was recovered in 12% of cases.

These results support the data previously reported and strongly suggest that M. globosa in its mycelial phase is the causative agent of PV.