Routine use of CHROMagar Candida medium for presumptive identification of Candida yeast species and detection of mixed fungal populations

Abstract

OBJECTIVE: To assess the value of the new differential culture medium CHROMagar Candida for routine investigation of clinical specimens. METHODS: During a whole year, 6150 clinical samples were plated on CHROMagar Candida medium. After incubation, the green colonies were considered to be Candida albicans. The colonies of other colors were identified using Bichrolatex-krusei, or by their assimilation pattern on ID 32C test strips and their morphology on rice cream-agar-Tween. RESULTS: Among the 6150 clinical samples, 1643 were positive for fungi. Aspergillus fumigatus and Geotrichum sp. were the predominant filamentous fungi isolated. Candida albicans was the most common species isolated (1274 of the positive samples; 77.5%), and Candida glabrata was the second most common yeast isolated (174 positive samples; 10.6%). Other yeast species were detected at lower frequencies, mainly Candida tropicalis (3.8%), Candida krusei (2.7%), Saccharomyces cerevisiae (2.7%) and Candida kefyr (2.3%), and 16 samples revealed a lipophilic species, Malassezia furfur. Mixed fungal populations accounted for 14.7% of the positive samples. Two or more yeast species were detected in 206 of the 242 specimens containing mixed fungal populations, and five yeast species were detected in one sample. Additionally, we did not observe significant differences in the isolation of yeasts or filamentous fungi from the 366 samples simultaneously plated on CHROMagar Candida and Sabouraud dextrose agar. Close agreement between the two culture media was observed for 89.9% of these samples. CONCLUSIONS: CHROMagar Candida medium was shown to be extremely helpful in a routine clinical mycology service, facilitating the detection of mixed cultures of yeasts and allowing direct identification of C. albicans, as well as rapid presumptive identification of the other yeasts: C. glabrata, C. tropicalis, C. krusei and S. cerevisiae. This chromogenic medium thus appears to be suitable as a primary culture medium, particularly for the mycologic surveillance of immunocompromised patients.