Tinea versicolor and Pityrosporum orbiculare: mycological investigations, experimental infections and epidemiological surveys.

In patients with tinea versicolor, Pityrosporum orbiculare was cultured from tinea versicolor lesions in 100%, from normal-looking skin in 80%, and from apparently healed lesions in 69%. P. orbiculare was isolated from normal skin in 85% of patients with seborrheic dermatitis and in 90% of volunteers. The best substrate for isolation of P. orbiculare was a peptone-glucose-yeast extract medium containing glycerol monostearate and Tween 80, overlaid with olive oil. Germ tubes were produced when P. orbiculare was incubated in an atmosphere containing air with 7% CO2. Cultures of P. orbiculare and P. ovale did not show any fluorescence in Wood's light. The in vitro activity of miconazole, clotrimazole, econazole, sodium omadine, and sodium thiosulphate against P. orbiculare was found to correlate to the good clinical effect of these drugs in tinea versicolor. In addition several substances used as solvents or in vehicles had an inhibitory activity against P. orbiculare in vitro. Inoculation with P. orbiculare under plastic occlusion on the glabrous follicle-rich inside of the rabbit ear resulted in a tinea versicolor-like lesion after I week in 3 of 4 animals. One week after inoculation with P. orbiculare under plastic occlusion, experimental infections similar to those found clinically in tinea versicolor were seen in 10 of 12 patients with a history of tinea versicolor and in 3 of 6 normal volunteers. It was not possible to produce experimental infections without occlusion. Spontaneous healing usually occurred. In a retrospective study of 232 patients and prospective survey of 48 patients regarding susceptibility factors in tinea versicolor a higher (10.4%) than expected (3.8%) connection to seborrheic dermatitis was found.