Cryptococcus neoformans serotype A and Cryptococcus gattii serotype B isolates differ in their susceptibilities to fluconazole and voriconazole

Abstract

This study presents antifungal susceptibility data for environmental isolates of Cryptococcus neoformans serotype A (n = 32) and Cryptococcus gattii serotype B (n = 18) to fluconazole and voriconazole employing disc diffusion and Etest methods. The disc diffusion test was performed on Mueller–Hinton agar as recommended by the Clinical and Laboratory Standards Institute (CLSI). For comparison, the disc diffusion test and Etest were also performed on RPMI-1640 agar supplemented with 2% glucose. The plates were incubated at 35 °C and read after 48 h. Comparison of geometric mean inhibition zone diameters revealed that C. gattii isolates were significantly less susceptible than C. neoformans isolates to fluconazole (P = 0.001) and voriconazole (P < 0.0001). Similar results were obtained on RPMI agar by disc diffusion test and Etest, showing significantly reduced susceptibility for C. gattii isolates. Notwithstanding differences in the susceptibilities of the two species to fluconazole and voriconazole, they appeared susceptible according to the CLSI breakpoints recommended for some Candida spp. To what extent these differences in the susceptibilities of C. neoformans and C. gattii impact on the therapeutic management of cryptococcosis is unclear, although some studies have reported less favourable response in cases caused by the latter species.