A Selective Medium for Isolation and Detection of Candida auris, an Emerging Pathogen

Identification of Candida auris is challenging and requires molecular or protein profiling-based approaches, availability of which is limited in many routine diagnostic laboratories, necessitating the development of a cost-effective, rapid, and reliable method of identification. The objective of this study was to develop a selective medium for C. auris identification. Eighteen C. auris and 30 non-C. auris yeasts were used for the standardization of the selective medium. Sodium chloride (10% to 13% concentration) and ferrous sulfate (8 mM to 15 mM) were added to yeast extract-peptone-dextrose (YPD) agar in various combinations followed by incubation at 37°C, 40°C, or 42°C for 2 to 3 days. For validation, 579 yeast isolates and 40 signal-positive Bactec blood culture (BC) broths were used. YPD agar comprising 12.5% NaCl and 9 mM ferrous sulfate incubated at 42°C for 48 h, named Selective Auris Medium (SAM), allowed selective growth of C. auris A total of 95% (127/133) of C. auris isolates tested grew on the standardized media within 48 h, and the remaining 6 isolates grew after 72 h, whereas the growth of 446 non-C. auris yeast isolates was completely inhibited. The specificity and sensitivity of the test medium were both 100% after 72 h of incubation. The positive and negative predictive values were also noted to be 100% after 72 h of incubation. The formulated selective medium can be used for the detection and identification of C. auris The SAM is inexpensive, can easily be prepared, and can be used as an alternative to molecular diagnostic tools in the clinical microbiology laboratory.