In vitro activity of five antifungal agents against clinical isolates of Saccharomyces cerevisiae

We evaluated the in vitro activity of fluconazole, itraconazole, ketoconazo le, 5-fluorocytosine and amphotericin B against 30 clinical isolates of Sac charomyces cerevisiae by a broth microdilution method, following the NCCLS recommendation. Testing was performed either in RPMI-1640 or yeast nitrogen base (YNB). YNB supported the growth of all isolates tested, while results in RPMI-1640 were not obtained for six isolates (20%). The MIC of all thre e azoles in YNB were one or two dilutions higher than those obtained in RPM I-1640 (P = 0.0001 for fluconazole and itraconazole, P = 0.03 For ketoconaz ole). Elevated MICs were observed for all three azoles, while all the isola tes were susceptible to 5-fluorocytosine and amphotericin B. All MIC values were confirmed by spectrophotometric reading. Six strains of S. cerevisiae isolated from the faeces and consecutive blood cultures from an AIDS patie nt over a 7-month period were typed by electrophoretic karyotyping (EK). EK showed the maintenance of the same karyotype over time suggesting that the faecal isolate changed from a colonizing to infection-causing strain. The relative resistance of S. cerevisiae to azole drugs as well as its ability to cause widespread infections may promote the emergence of this species as a pathogen in immunosuppressed patients.