MULTICENTER EVALUATION OF BROTH MICRODILUTION METHOD FOR SUSCEPTIBILITY TESTING OF CRYPTOCOCCUS-NEOFORMANS AGAINST FLUCONAZOLE

We have developed a microdilution method for measuring the susceptibil ity of Cryptococcus neoformans to fluconazole. The present study evalu ated the interlaboratory agreement of the results for the microdilutio n method obtained at three different sites and compared this method wi th the National Committee for Clinical Laboratory Standards M27-P refe rence method. Excellent interlaboratory agreement among the results ob tained at the three sites was achieved with this method (83 and 96% ag reement within 1 and 2 log(2) dilutions, respectively), An overall agr eement of 90% between the microdilution method and the M27-P method wa s observed, demonstrating the comparability of the two methods, Howeve r, there are inherent problems with the M27-P method in relation to me asuring C. neoformans susceptibility, including suboptimal growth of t he organism in RPMI 1640, a longer incubation period, and a narrow ran ge of MICs. On the basis of these data, the microdilution method teste d in this study is recommended for inclusion in the National Committee for Laboratory Standards method for testing the antifungal susceptibi lity of C. neoformans.