Preliminary evaluation of a semisolid agar antifungal susceptibility test for yeasts and molds

This report presents a semisolid agar antifungal susceptibility (SAAS) meth od for the rapid susceptibility screening of yeasts and molds, The reproduc ibility and accuracy of the SAAS method were assessed by comparing the MICs of amphotericin B and fluconazole obtained for 10 candidate quality contro l (QC) American Type Culture Collection yeast strains in greater than or eq ual to 15 replicates with those found by six independent laboratories using the National Committee for Clinical Laboratory Standards (NCCLS) M27-P bro th macrodilution method (M. A. Pfaller et al., J. Clin. Microbiol. 33:1104- 1107, 1995), Overall, 96% of MICs for both drugs fell within 1 log(2) dilut ion of the modal MIC for each strain. The MICs for amphotericin B showed 99 % agreement with the NCCLS proposed QC ranges within 1 log, dilution. Likew ise, the MICs for fluconazole at greater than or equal to 75% growth reduct ion showed 99% agreement for seven strains. Three strains, Candida albicans ATCC 24333 and ATCC 76615 and Candida tropicalis ATCC 750, showed a less s harp fluconazole endpoint at greater than or equal to 75% growth reduction, but at >50% growth reduction, the agreement was 98% within 1 log(2) diluti on of tbe proposed range, The MIC agreement within the proposed range for t he suggested QC strains Candida parapsilosis ATCC 22019 and Candida krusei ATCC 6258 was 100% for fluconazole and 100% within 1 log(2) dilution of the proposed range for amphotericin B. The SAAS method demonstrated the suscep tibility or resistance of 25 clinical isolates of filamentous fungi such as Aspergillus fumigatus to amphotericin B, itraconazole, and fluconazole, us ually within 48 h, Although the results are preliminary, this SAAS method i s promising as a rapid and cost-effective screen and is worthy of concerted investigation.