Discriminative power of fatty acid methyl ester (FAME) analysis using the Microbial Identification System (MIS) for Candida (Torulopsis) glabrata andSaccharomyces cerevisiae

Candida (Torulopsis) glabrata is frequently isolated in cases of fungal inf ection and commonly shows acquired or innate fluconazole resistance. Saccha romyces cerevisiae, an emerging opportunistic yeast pathogen, causes seriou s systemic infections in immunocompromised, and vaginitis and superficial i nfections in immunocompetent patients. For both species reliable identifica tion in the routine laboratory is mandatory, but species identification of strains, e.g. trehalose-negative C. glabrata, may be difficult. Therefore, gas-liquid chromatography (GLC) of whole cell fatty acid methyl ester (FAME ) profiles, that is independent of assimilation profiles of strains and sui table for reliable and rapid identification of clinically important yeasts, was applied. However, frequent misidentification of C. glabrata as S. cere visiae has been reported when using the Yeast Clinical Database of MIS. Acc uracy of MIS identification may be strongly influenced by the amounts of ce ll mass analyzed. Therefore, the present study compared the MIS results of these two yeasts achieved with different cell masses. Primarily we optimize d, especially with respect to cost-effectiveness, the recommended streaking technique yielding a maximal recovery of 90-130 mg of cell mass from one p late, enabling testing of poor growing strains of C. glabrata. For all C. g labrata strains tested (n = 10) the highest identification scores (SI [Simi larity Index] range 0.525-0.963, median 0.832) were achieved with 30 to 45 mg of cell mass. Only 5 of 10 S. cerevisiae strains revealed good library c omparisons (SI greater than or equal to 0.5) when using 30 mg of cell mass, whereas with 45 mg all strains but two revealed this SI-level. For S. cere visiae a higher amount of cell mass processed (up to 90 mg) was correlated with better identification scores (SI range using 90 mg: 0.464-0.870, media n, 0.737). Several passages prior to FAME analysis of C. glabrata strains o n recommended media revealed narrowing of SI ranges, but differences in SI values were not statistically significant. (C) 2000 Elsevier Science Inc. A ll rights reserved.