Heteroresistance to fluconazole among isolates of Cryptococcus neoformans in Northern Thailand

We had determined that 190 Cryptococcus neoformans isolates (104 clinical and 86 environmental isolates from northern Thailand) were all susceptible to amphotericin B, fluconazole, itraconazole and ketoconazole. Of 14 selected isolates, one clinical isolate (CN4969) exhibited heterogeneity in fluconazole resistance, which produced two subpopulations of the fluconazole-resistant (CN4969HR) and -susceptible (CN4969S) subpopulations. To clarify the molecular mechanisms of fluconazole resistance, the expression of drug resistance genes was determined by using reverse transcription-polymerase chain reaction (RT-PCR). Both the ERG11 and MDR1 transcript levels showed at least a 2-fold increase in CN4969HR isolate compared to the fluconazole-susceptible isolates (H99, CN4901 and CN4969S), whereas the expression level of theAFR1 gene in CN4969HR was equivalent to that of isolates H99, CN4901 or CN4969S. Collectively, this study demonstrates the existing of the fluconazole heteroresistant population among clinical isolates of C. neoformans in northern part of Thailand and molecular mechanism of fluconazole-susceptible and resistant isolates.   Key words: Heteroresistance, fluconazole, C. neoformans, Thailand.