Phenotypic Switching and Genetic Diversity of Cryptococcus neoformans

Abstract

Niger seed agar was used as a primary plating medium for the isolation of Cryptococcus neoformans from cerebrospinal fluid specimens from AIDS patients with untreated primary cryptococcosis. The medium was used as the primary means to detect variations in the colony morphology of the yeast. To search for phenotypic and genetic variations, nine patients individually harboring two or three types of colony morphology were studied. Intraindividual isolates 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 different. Intraindividual isolates from three patients had minor karyotype differences, and one showed a dramatic chromosomal length polymorphism. In addition, three serial isolates from a patient with two episodes of infection showed 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 evidence suggesting that (i) in humans, C. neoformans may undergo phenotypic and genetic changes during early infection prior to antifungal agent administration; (ii) dramatic variations in electrophoretic karyotypes and in phenotypes, as demonstrated during the early infection of one patient, may be due to infection by different strains; and (iii) the use of niger seed agar as a primary plating medium is useful for studying antifungal susceptibility, phenotypic switching, genetic diversity, and multiplestrain infections.

Dual Infections with Pigmented and Albino Strains ofCryptococcus neoformansin Patients with or without Human Immunodeficiency Virus Infection in India

“…Subsequently, a larger study of serial isolates from 33 individuals with HIV documented the persistence of a single C. neoformans isolate and failed to find evidence for dual infection or reinfection with a second strain (2). Nevertheless, additional instances of dual infections and acquisition of a second strain of C. neoformans have been described (16,21,37,38). Since routine typing of isolates is performed on one or two selected colonies, a strain present in low numbers relative to a second strain might not be detected.…”

Phenotypic switching in Cryptococcus neoformans

“…There is no obvious association with mating type or serotype (Jain et al, 2005). In summary, many studies demonstrate that phenotypic changes occur rapidly during chronic infection (Currie et al, 1995;Fries et al, 1996;Sukroongreung et al, 2001). Phenotypic switching is one mechanism that can facilitate microevolution.…”

Role of Phagocytosis in the Virulence ofCryptococcus neoformans

“…These colonies with an altered morphology, e.g., opaque instead of white or mucoid instead of smooth yeast colonies, result from the differential expression of specific genes or factors which in turn may affect the course of infection. Phenotypic switching occurs in many microorganisms, including bacteria (Mycobacterium avium [14] and Mycoplasma [110]), viruses (human immunodeficiency virus [HIV] [12]), protozoa (Trypanosoma brucei [104] and Plasmodium falciparum [79]), and fungi (C. albicans [96,97,105], Candida glabrata [10], and C. neoformans [34,101,112]). In C. neoformans, phenotypic switching occurs in vivo and influences the outcome of infection (35).…”