Specific immunological test for the rapid identification of members of the genus Histoplasma

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Abstract
A sensitive and specific immunological method was developed for rapid identification of the mycelial forms of Histoplasma capsulatum var. capsulatum, H. capsulatum var. duboisii and H. farciminosum, and for separation of these pathogenic fungi from morphologically similar hyphomycetes and other fungal pathogens. This method is based on the fact that all of the Histoplasma spp. produce H and M histoplasmin antigens, the other fungi do not. Inocula consisting of heavy mycelial growth from a pure full-grown culture were transferred to flasks containing small volumes of brain heart infusion [BHI] broth. These cultures were placed on a shaker and grown at 25.degree. C. Using microimmunodiffusion and antisera containing antibodies to H and M precipitinogens, exoantigens were detected in 3-day-old BHI culture supernatants concentrated 25 and 50 times. The ability of the procedure to identify Histoplasma spp. was evaluated by testing 96 unknown mycelial cultures that grossly or microscopically resembled Histoplasma spp. Three- and 6-day-old concentrated culture supernatants prepared from each unknown were tested against rabbit anti-Arthroderma tuberculatum, Chrysosporium keratinophilum, H. capsulatum var. duboisii, and Corynascus (Thielavia) sepedonium sera and human histoplasmosis case serum. Each unknown was also identified by conventional laboratory procedures involving cultural and, where necessary, in vivo studies. In the comparative evaluation the immunological test was 100% sensitive. It permitted the accurate generic identification of the Histoplasma spp. within 5 days, in contrast to the average 33 days required by routine mycological procedures.