Candida auris Clinical Isolates from South Korea: Identification, Antifungal Susceptibility, and Genotyping

Abstract

Candida auris is an emerging worldwide fungal pathogen. Over the past 20 years, 61 patient isolates of C. auris (4 blood and 57 ear) have been obtained from 13 hospitals in Korea. Here, we reanalyzed those molecularly identified isolates using two matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) systems, including Biotyper and Vitek MS, followed by antifungal susceptibility testing, sequencing of the ERG11 gene, and genotyping. With a research-use-only (RUO) library, 83.6% and 93.4% of the isolates were correctly identified by Biotyper and Vitek MS, respectively. Using an in vitro diagnostic (IVD) library of Vitek MS, 96.7% of the isolates were correctly identified. Fluconazole-resistant isolates made up 62.3% of the isolates, while echinocandin- or multidrug-resistant isolates were not found. Excellent essential (within two dilutions, 96.7%) and categorical agreements (93.4%) between the Clinical and Laboratory Standards Institute (CLSI) and Vitek 2 (AST-YS07 card) methods were observed for fluconazole. Sequencing ERG11 for all 61 isolates revealed that only 3 fluconazole-resistant isolates showed the Erg11p amino acid substitution K143R. All 61 isolates showed identical multilocus sequence typing (MLST). Pulsed-field gel electrophoresis (PFGE) analyses revealed that both blood and ear isolates had the same or similar patterns. These results show that MALDI-TOF MS and Vitek 2 antifungal susceptibility systems can be reliable diagnostic tools for testing C. auris isolates from Korean hospitals. The Erg11p mutation was seldom found among Korean isolates of C. auris, and multidrug resistance was not found. Both MLST and PFGE analyses suggest that these isolates are genetically similar.

Keywords: Candida auris; MALDI-TOF MS; antifungal susceptibility testing; genotyping.

FIG 1

Representative PFGE patterns of Candida auris obtained by electrophoretic karyotyping (EK) and restriction endonuclease analyses of genomic DNA using NotI (REAG-N) for blood (isolates B1 to B4) and ear (isolates E1 to E9) isolates of C. auris from Korean hospitals, and ten C. auris isolates with representatives from each of the four clades (A1 to A10, C. auris AR0381 to C. auris AR0390, respectively) provided by the U.S. Centers for Disease Control and Prevention (CDC). See Tables 3 and 4 for detailed information on each isolate. Two sequential blood isolates each from the same patient (isolates B1 from patient 1, isolates B2 from patient 2, and isolates B3 from patient 3) had the same EK and the same REAG-N patterns. All isolates from Korean hospitals exhibited the same EK pattern and showed the same or similar REAG-N patterns, which were different from those of ten CDC C. auris isolates. M, Saccharomyces cerevisiae DNA concatemers that served as a molecular size marker.