Several molecular mechanisms of azole resistance have been described, mainly, in C. albicans. However, the molecular mechanism of fluconazole (FZ)-resistant strains of C. neoformans (Cn) has not been elucidated. In this study, recurrent isolates of Cn were recovered from a patient with AIDS with 5 symptomatic episodes of cryptococcal meningitis and exposed to FZ therapy during a period of 14 months. Isolates from the 1st to the 4th episode had FCZ-MICs between 1-2 µg/ml and were classified as susceptible. Isolate from the 5th episode showed an MIC of 16 µg/ml and was considered as resistant. DNA fingerprinting showed that all five isolates were isogenic, meaning that all episodes of cryptococcal meningitis were caused by the same strain. In order to research into the molecular mechanism that rendered the last resistant strain, we amplified by PCR and sequenced the gene encoding 14a-sterol demethylase (ERG11) from all five isogenic strains. The first four strains isolates (FCZ-susceptible) did not show any base change in the entire ERG11 sequence. However, the 5th strain (FZ-resistant) exhibited a point mutation (g1855t) responsible for a substitution of glycine 484 per serine (G484S), located at a very conserved region of the ERG11 protein. The equivalent amino acid substitution, located at G464S of C. albicans, has been previously related to FZ resistance in sequential isolates from patients under long FZ treatment. In Cn this is the first report that relate punctual mutations to azole resistance. However, in C. albicans FZ resistance has been matched to multiple mechanisms, and the possibility of involvement of another molecular mechanisms of resistance should be evaluated in these strains.
Full conference title:
43rd Interscience Conference on Antimicrobial Agents
- ICAAC 43rd