Comparative evaluation of Sensititre YeastOne and VITEK 2 against the Clinical and Laboratory Standards Institute M27-E4 reference broth microdilution method for the antifungal susceptibility testing of Cryptococcus neoformans and Cryptococcus gattii

Abstract

The present study collected 280 isolates of Cryptococcus neoformans and 22 isolates of Cryptococcus gattii and evaluated the consistencies between Sensititre YeastOne (SYO), VITEK 2, and the reference broth microdilution (BMD) method for the antifungal susceptibility testing of fluconazole, voriconazole, and flucytosine. For amphotericin B, SYO was replaced with the BIO KONT amphotericin B microbroth dilution kit. The essential agreements (EAs) by SYO and VITEK 2 for C. neoformans var. grubii and C. neoformans var. neoformans were 98.15-99.63% and 88.89-100%, respectively, with fluconazole, voriconazole, and flucytosine. The EA for C. gattii VG Ⅰ against fluconazole was 29.41% by VITEK 2, while the other EAs for C. gattii strains were 100% by SYO and VITEK 2. The categorical agreements (CAs) by SYO and VITEK 2 for C. neoformans and C. gattii were 94.12-100%, while VITEK 2 failed to distinguish 5/6 fluconazole-resistant non-wild-type C. neoformans var. grubii isolates; this finding confirmed the limitation of testing fluconazole against C. neoformans as documented in the manufacturer's package insert. The EAs for amphotericin B were 97.42-100% for C. neoformans and C. gattii, but the CAs were 17.65-60% by BIO KONT and VITEK 2. Thus, SYO can be used for susceptibility testing of C. neoformans and C. gattii against fluconazole, voriconazole, and flucytosine, and VITEK 2 can be used for susceptibility testing of C. neoformans against voriconazole and flucytosine. Further studies using amphotericin B-resistant isolates are required to assess the agreement between VITEK 2, BIO KONT, and BMD.

Lay summary: Sensititre YeastOne showed a good agreement with the CLSI broth microdilution method for C. neoformans and C. gattii against voriconazole and flucytosine. The limitation regarding fluconazole testing against C. neoformans documented in VITEK 2 manufacturer's package insert was confirmed.

Keywords: CLSI; Cryptococcus; Sensititre YeastOne; VITEK 2; antifungal susceptibility.