LAUSR

What explains the origin, emergence, and persistence of Candida auris? Candida auris is a major emerging human fungal pathogen that was first reported in 2009 as an isolate from the ear canal of a patient in Japan [1]. Since this initial report, C. auris has grown to represent a “serious threat” in healthcare settings, as indicated by the United States Centers for Disease Control (CDC) and is now on the World Health Organization (WHO) fungal priority pathogen list, described as the “most wanted” critical pathogen [2,3]. However, many questions remain about the emergence, spread, and persistence of C. auris. In particular, the sudden, simultaneous, and independent worldwide emergence of 5 C. auris clades in completely separate geographical regions is a profound puzzle. One hypothesis suggests that C. auris was not detected until recently as a consequence of nonreliance on conventional phenotypic typing methods. Correct identification of C. auris is crucial for the adequate treatment and control of outbreaks and has been a frequent limitation. C. auris can be grown under similar conditions to those of other Candida species and single colonies can be obtained on conventional Sabouraud dextrose agar following 24 hours of incubation at 30 to 35 ̊C [4]. However, the ability of C. auris to grow at temperatures up to 42 ̊C differentiates it from other Candida species [5]. In clinical microbiology laboratories C. auris is frequently undetected, as 90% of isolates are misdiagnosed as Candida haemulonii, Candida famata, Candida guilliermondii, Candida lusitaniae, Candida parapsilosis, Candida sake, Rhodotorula glutinis, Candida duobushaemulonii, Candida catenulata, Candida tropicalis, or Saccharomyces cerevisiae, with commercial identification systems that utilize biochemical phenotyping [6–8]. C. auris appears white, pink, or purple on conventional CHROMagar Candida chromogenic medium (Becton-Dickinson, Rungis, France) but on CAN2 plates (bioMérieux, Capronne, France), colonies are initially white, but later appear as a light reddish pink color [5]. Recently, CHROMagar Candida Plus (Becton-Dickinson, Rungis, France) and HiCrome C. auris MDR selective agar (HiMedia, Mumbai, India) have been found to be highly specific and sensitive for the isolation and identification of C. auris after 36 to 48 hours of incubation [9–11]. FDA-approved methods such as MALDI-TOF mass spectrometry, combined with upto-date spectra databases, as well as the user-made MSI library (Paris, France) have also been used for the definitive identification of C. auris [12]. Finally, a combination of D1/D2 and ITS sequencing have proven to be the gold standard for C. auris identification [13]. While recent advances in fungal molecular diagnostics have improved C. auris detection and identification, the hypothesis that C. auris was not accurately detected is not alone sufficient to explain the PLOS PATHOGENS