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

Abstract

Identification of <i>Candida auris</i> 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 <i>C. auris</i> identification. Eighteen <i>C. auris</i> and 30 non-<i>C. auris</i> 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 <i>C. auris</i> A total of 95% (127/133) of <i>C. auris</i> 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-<i>C. auris</i> 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 <i>C. auris</i> The SAM is inexpensive, can easily be prepared, and can be used as an alternative to molecular diagnostic tools in the clinical microbiology laboratory.