Aberrant Histoplasma capsulatum. Confirmation of identity by a chemiluminescence-labeled DNA probe.

A cottony, light tan, filamentous fungus with pear-shaped microconidia and lacking tuberculated macroconidia was isolated from a bronchial lavage specimen. Subculture on several media at 37 degrees C failed to convert the fungus to a yeast form after several weeks; attempts at in vivo conversion in mice were also unsuccessful. Sera obtained several months apart showed M bands with Histoplasma capsulatum (HC) antigen by immunodiffusion and an increase in complement fixation titers with mycelial and yeast phase antigens of HC. Parallel identity was obtained on two occasions with exoantigen culture confirmation reagents for HC from Immuno-Mycologics as well as one of identity with Nolan reagents. Extracts from four Chrysosporium spp. strains had no identity reactions with HC with either kit. The fungus was identified as HC by the Accuprobe Histoplasma chemiluminescence-labeled DNA probe directed at ribosomal RNA, whereas all four Chrysosporium spp. isolates tested negative. DNA probes are a fast and accurate method to confirm the identity of aberrant fungal isolates.