Cryptococcus neoformans-Cryptococcus gattii Species Complex: an International Study of Wild-Type Susceptibility Endpoint Distributions and Epidemiological Cutoff Values for Amphotericin B and Flucytosine

Abstract

ABSTRACTClinical breakpoints (CBPs) are not available for theCryptococcus neoformans-Cryptococcus gattiispecies complex. MIC distributions were constructed for the wild type (WT) to establish epidemiologic cutoff values (ECVs) forC. neoformansandC. gattiiversus amphotericin B and flucytosine. A total of 3,590 amphotericin B and 3,045 flucytosine CLSI MICs forC. neoformans(including 1,002 VNI isolates and 8 to 39 VNII, VNIII, and VNIV isolates) and 985 and 853 MICs forC. gattii, respectively (including 42 to 259 VGI, VGII, VGIII, and VGIV isolates), were gathered in 9 to 16 (amphotericin B) and 8 to 13 (flucytosine) laboratories (Europe, United States, Australia, Brazil, Canada, India, and South Africa) and aggregated for the analyses. Additionally, 442 amphotericin B and 313 flucytosine MICs measured by using CLSI-YNB medium instead of CLSI-RPMI medium and 237 Etest amphotericin B MICs forC. neoformanswere evaluated. CLSI-RPMI ECVs for distributions originating in ≥3 laboratories (with the percentages of isolates for which MICs were less than or equal to ECVs given in parentheses) were as follows: for amphotericin B, 0.5 μg/ml forC. neoformansVNI (97.2%) andC. gattiiVGI and VGIIa (99.2 and 97.5%, respectively) and 1 μg/ml forC. neoformans(98.5%) andC. gattiinontyped (100%) and VGII (99.2%) isolates; for flucytosine, 4 μg/ml forC. gattiinontyped (96.4%) and VGI (95.7%) isolates, 8 μg/ml for VNI (96.6%) isolates, and 16 μg/ml forC. neoformansnontyped (98.6%) andC. gattiiVGII (97.1%) isolates. Other molecular types had apparent variations in MIC distributions, but the number of laboratories contributing data was too low to allow us to ascertain that the differences were due to factors other than assay variation. ECVs may aid in the detection of isolates with acquired resistance mechanisms.