Collaborative evaluation in seven laboratories of a standardized micromethod for yeast susceptibility testing

Abstract

The new micromethod for yeast susceptibility testing, MYCOTOTAL, was evaluated with 10 reference strains in seven laboratories. Ready-to-use microtitration plates and the same synthetic medium were used with two dilutions of imidazoles, flucytosine, and amphotericin B, permitting the categorization of each strain as susceptible, intermediate, or resistant. The results were compared with the MIC for each reference strain, and the repeatability and reproducibility were evaluated. The yeasts tested presenting different patterns of susceptibilities in reference MICs included six strains of Candida albicans, two strains of Candida tropicalis, one strain of Candida parapsiosis, and one strain of Torulopsis glabrata. For 4,200 antifungal agent-yeast results, the repeatability was 99.3% and the reproducibility was 96.3%. The correlation between the reference MICs and the category results was 91.5% for seven laboratories (and 92.7% for six laboratories excluding the laboratory which did not follow exactly the same protocol). We observed only 7.9% minor discrepancies, 0.5% (0.29% for six laboratories) major discrepancies, and 0.1% uninterpretable results. The percentages of concording results were similar for each strain and each antifungal agent tested. The overall results indicated that MYCOTOTAL was a reliable and reproducible method, well correlated with reference MICs. This ready-to-use micromethod with the same medium for all antifungal agents would be an important step in the necessary standardization of yeast susceptibility testing.

An evaluation of seven methods of testing in vitro susceptibility of clinical yeast isolates to fluconazole

“…The difficulties of determining reliable susceptibility results for fungi with traditional in vitro tests have been extensively reported [11,13,[15][16][17][18][19][20][21][22][23]. Major limitations of all test systems investigated in this study were partly due to insufficient or poor growth of several clinically important yeasts.…”

“…Mycototal@ medium. This is a semisolid culture medium, provided by the manufacturer, based on yeast nitrogen base supplemented with a vitamin solution as described by Guinet et al [12,13].…”

Lack of correlation of 24- vs. 48-h itraconazole minimum inhibitory concentrations with microbiological and survival outcomes in a guinea pig model of disseminated candidiasis

“…The high prevalence of opportunistic fungal infections 1,2 combined with reports of increasing resistance to the available antifungal agents [3][4][5][6] has crystallised the need for clinically relevant methods for antifungal susceptibility testing. In 1983, the National Committee for Clinical Laboratory Standards (NCCLS; currently named as Clinical and Laboratory Standards Institute; CLSI) responded to this need by establishing a subcommittee to develop standardised antifungal susceptibility testing procedures and as a result of many collaborative and individual [7][8][9][10][11][12][13][14][15] studies, an approved reference method for broth dilution antifungal testing for yeast was developed which is known as the CLSI M27. 16 It is important, however, to realise that the clinical relevance of the M27 methodology has not been fully established.…”

Evaluation of latex reagents for rapid identification of Candida albicans and C. krusei colonies

“…The widespread use of broad-spectrum antibiotics and the rising number of immunocompromised patients are the major reasons leading saprophytic yeasts to become pathogenic and contributing to the emergence of new opportunistic yeasts (1,20,44). Moreover, opportunistic yeasts demonstrate various degrees of in vivo and in vitro resistance to common antifungal agents (21,29), and it is now well known that strains of Candida lusitaniae (19) and Candida krusei and Candida glabrata (17,20,44) are relatively resistant to amphotericin B and fluconazole, respectively. However, Candida albicans remains the most common species isolated, representing between 60 and 80% of all clinical isolates of yeasts and exhibiting a high sensitivity to antifungal agents (11,17,30).…”