Etiological significance of Pityrosporum orbiculare in tinea versicolor.

Strains of Pityrosporum orbiculare were isolated from the Malassezia furfur infected scales of ten cases of tinea versicolor. The morphologic characteristics of M. furfur in the scales and P. orbiculare in culture are described. Specific antiserum to P. orbiculare (strain #7) was produced by injecting the organism into the foot pads of guinea pigs. The capacity of the serum to combine with P. orbiculare and M. furfur was determined by fluorescent antibody staining. These investigations have shown morphologic and antigenic relationships between P. orbiculare and M. furfur, the latter the etiologic agent of tinea versicolor.