Antifungal susceptibility profiles of Coccidioides immitis and Coccidioides posadasii from endemic and non-endemic areas

Abstract

Coccidioidomycosis is a systemic fungal infection endemic in Southwestern United States, Mexico, Central and South America. The causal agents are Coccidioides immitis and C. posadasii. A large number of cases of coccidioidomycosis in New York State residents were identified. We compared susceptibility profiles of these isolates and of C. immitis isolates from California using mycelial phase inoculum and CLSI (NCCLS) M38-A broth microdilution protocol. Minimum fungicidal concentrations (MFC) were also determined. Results indicated that geometric mean MICs of amphotericin B (AMB, 0.06 microg/ml), fluconazole (FLC, 8.0 microg/ml), itraconazole (ITC, 0.07 microg/ml), ketoconazole (KTC, 0.04 microg/ml), voriconazole (VRC, 0.04 microg/ml), posaconazole (PSC, 0.17 microg/ml) and caspofungin (CSP, 0.15 microg/ml) were in susceptible range as per breakpoints published for pathogenic Candida species. However, geometric MFC for FLC was relatively higher (52.4 microg/ml). Also, no significant difference in MIC and MFC values was evident for C. immitis and C. posadasii isolates. In conclusion, current methods for antifungal susceptibility testing yield reproducible profiles for Coccidioides species, which appear to be highly susceptible to most antifungal agents.