Molecular typing of Cryptococcus neoformans: taxonomic and epidemiological aspects

Pulsed-field gel elecrophoresis (PFGE), randomly amplified polymorhic DNA (RAPD) analysis, serotype, and killer toxin sensitivity patterns of a wide range of saprobic, clinical, and veterinary isolates of both varieties of Cryptococcus neoformans were examined. C. neoformans var. neoformans and C. neoformans var. gattii differed in chromosomal makeup, RAPD patterns, and killer sensitivity patterns. These result suggest that there are two separate species rather than two varieties. No clear genetic or phenotypic differences were observed among the clinical, saprobic, and verterianary isolates within each taxon. The serotypes differed substantially in their RAPD characteristics. Geographical clustering was observed among the isolates of C. neoformans var. gattii, but not among the isolates of C. neoformans var. neoformans. The isolates of each taxon that originated from resteted geographical areas often had identical or similar karyotpes and RAPD patterns, suggesting that clonal reproduction had occurred. The combination of PFGE and RAPD analysis allowed us to distinguish almost all isoltes. This combination of techniques is recommended for further research on epidemiological, ecological, and population issues.