Multidrug-Resistant Candida auris Misidentified as Candida haemulonii: Characterization by Matrix-Assisted Laser Desorption Ionization–Time of Flight Mass Spectrometry and DNA Sequencing and Its Antifungal Susceptibility Profile Variability by Vitek 2, CLSI Broth Microdilution, and Etest Method

Abstract

Candida aurisis a multidrug-resistant yeast that causes a wide spectrum of infections, especially in intensive care settings. We investigatedC. aurisprevalence among 102 clinical isolates previously identified asCandida haemuloniiorCandida famataby the Vitek 2 system. Internal transcribed spacer region (ITS) sequencing confirmed 88.2% of the isolates asC. auris, and matrix-assisted laser desorption ionization–time of flight mass spectrometry (MALDI-TOF MS) easily separated all related species,viz.,C. auris(n= 90),C. haemulonii(n= 6),C. haemuloniivar.vulnera(n= 1), andCandida duobushaemulonii(n= 5). Thein vitroantifungal susceptibility was determined using CLSI broth microdilution (CLSI-BMD), the Vitek 2 antifungal susceptibility test, and the Etest method.C. aurisisolates revealed uniformly elevated fluconazole MICs (MIC50, 64 μg/ml), and an alarming percentage of isolates (37%) exhibited elevated caspofungin MICs by CLSI-BMD. Notably, 34% ofC. aurisisolates had coexisting elevated MICs (≥2 μg/ml) for both fluconazole and voriconazole, and 10% of the isolates had elevated coexisting MICs (≥2 μg/ml) to two additional azoles, i.e., posaconazole and isavuconazole. In contrast to reduced amphotericin B MICs by CLSI-BMD (MIC50, 1 μg/ml) forC. auris, elevated MICs were noted by Vitek 2 (MIC50, 8 μg/ml), which were statistically significant.Candida aurisremains an unnoticed pathogen in routine microbiology laboratories, as 90% of the isolates characterized by commercial identification systems are misidentified asC. haemulonii. MALDI-TOF MS proved to be a more robust diagnostic technique for rapid identification ofC. auris. Considering that misleading elevated MICs of amphotericin B by the Vitek AST-YS07 card may lead to the selection of inappropriate therapy, a cautionary approach is recommended for laboratories relying on commercial systems for identification and antifungal susceptibility testing of rare yeasts.