title: Detection of amphotericin B resistance in Candida haemulonii and closely related species by use of the Etest, Vitek-2 yeast susceptibility system, and CLSI and EUCAST broth microdilution methods.
abstract: The emerging fungal pathogens Candida haemulonii and Candida pseudohaemulonii often show high-level resistance to amphotericin B (AMB). We compared the utilities of five antifungal susceptibility testing methods, i.e., the Etest using Mueller-Hinton agar supplemented with glucose and methylene blue (Etest-MH), the Etest using RPMI agar supplemented with glucose (Etest-RPG), the Vitek-2 yeast susceptibility system, and the Clinical and Laboratory Standards Institute (CLSI) and European Committee on Antimicrobial Susceptibility Testing (EUCAST) broth microdilution methods, for the detection of AMB-resistant isolates of C. haemulonii and closely related species. Thirty-eight clinical isolates (8 C. haemulonii, 10 C. pseudohaemulonii, and 20 Candida auris isolates) were analyzed. Of the 18 C. haemulonii and C. pseudohaemulonii isolates, 18, 15, 18, 10, and 9 exhibited AMB MICs of >1 μg/ml by the Etest-MH, Etest-RPG, Vitek-2, CLSI, and EUCAST methods, respectively. All 20 C. auris isolates showed AMB MICs of ≤1 μg/ml by all five methods. Of the methods, the Etest-MH generated the broadest distribution of AMB MICs for all 38 isolates and showed the best discrimination between the C. haemulonii and C. pseudohaemulonii isolates (4 to 32 μg/ml) and those of C. auris (0.125 to 0.5 μg/ml). Taking the Etest-MH as the reference method, the essential agreements (within two dilutions) for the Etest-RPG, Vitek-2, CLSI, and EUCAST methods were 84, 92, 55, and 55%, respectively; the categorical agreements were 92, 92, 79, and 76%, respectively. This study provides the first data on the efficacy of the Etest-MH and its excellent agreement with Vitek-2 for discriminating AMB-resistant from AMB-susceptible isolates of these Candida species.
authors.affiliation: Department of Laboratory Medicine, Chonnam National University Medical School, Gwangju, South Korea. shinjh@chonnam.ac.kr
authors.forename: Jong Hee
authors.initials: JH
authors.lastname: Shin
authors.forename: Mi-Na
authors.initials: MN
authors.lastname: Kim
authors.forename: Sook Jin
authors.initials: SJ
authors.lastname: Jang
authors.forename: Min Young
authors.initials: MY
authors.lastname: Ju
authors.forename: Soo Hyun
authors.initials: SH
authors.lastname: Kim
authors.forename: Myung Geun
authors.initials: MG
authors.lastname: Shin
authors.forename: Soon Pal
authors.initials: SP
authors.lastname: Suh
authors.forename: Dong Wook
authors.initials: DW
authors.lastname: Ryang
mesh_terms: D000666:Amphotericin B / Q000494:pharmacology*; D000935:Antifungal Agents / Q000494:pharmacology*; D002175:Candida / Q000187:drug effects*; D025141:Drug Resistance, Fungal; D006801:Humans; D008826:Microbial Sensitivity Tests / Q000379:methods; D009172:Mycology / Q000379:methods*
chemical_list: D000935:Antifungal Agents; D000666:Amphotericin B