Phenotypic switching and genetic diversity of Cryptococcus neoformans

Niger seed agar was used as a primary plating medium for the isolation of C ryptococcus neoformans from cerebrospinal fluid specimens from AIDS patient s with untreated primary cryptococcosis, The medium was used as the primary means to detect variations in the colony morphology of the yeast. To searc h for phenotypic and genetic variations, nine patients individually harbori ng two or three types of colony morphology mere studied. Intraindividual is olates from nine patients had minor variations in the API 20C profile, and the MICs of one or more antifungal agents (amphotericin B, fluconazole, and itraconazole) for isolates from three patients were significantly differen t. Intraindividual isolates from three patients had minor karyotype differe nces, and one showed a dramatic chromosomal length polymorphism, In additio n, three serial isolates from a patient with two episodes of infection show ed similar karyotypes, confirming persistent infection by the same strain. Random amplified polymorphic DNA products were identical for all isolates ( including three isolates from a relapse case). Our results provided evidenc e suggesting that (i) in humans, C, neoformans may undergo phenotypic and g enetic changes during early infection prior to antifungal agent administrat ion; (ii) dramatic variations in electrophoretic karyotypes and in phenotyp es, as demonstrated during the early infection of one patient, may be due t o infection by different strains; and (iii) the use of niger seed agar as a primary plating medium is useful for studying antifungal susceptibility, p henotypic switching, genetic diversity, and multiple-strain infections.