Superficial Phaeohyphomycosis Caused by Aureobasidium melanogenum Mimicking Tinea Nigra in an Immunocompetent Patient and Review of Published Reports

Aureobasidium pullulans is a ubiquitous black yeast-like fungus belonging to order Dothideales. It was regarded as a contaminant, but is now considered a pathogen causing a wide range of human infections. We report a case of superficial phaeohyphomycosis in an immunocompetent patient with clinical presentations mimicking tinea nigra. On microscopic examination of lesion scales, multiple thick-walled, pigmented oval spores with septa were noted. A fungus with black mucoid colonies was repeatedly isolated from the lesions during the treatment course. This fungus was identified as A. melanogenum on the basis of morphological characteristics and subsequently confirmed by sequencing internal transcribed spacers of ribosomal DNA. The clinical presentations and microscopic findings of lesion scales were considerably similar to those of tinea nigra. However, fungal culturing proved that the causative pathogen was A. melanogenum rather than Hortaea werneckii. The patient might have acquired this infection during gardening activities. We also reviewed reported cases of cutaneous A. pullulans infection.