Utility of CHROMagar™ Candida Plus for presumptive identification of Candida auris from surveillance samples

Abstract

Candida auris is a nosocomial fungal pathogen of prime importance due to its global emergence and rapid spread in healthcare facilities worldwide. One important concern is that routine, conventional methods fail to identify C. auris. While molecular and protein-based assays accurately detect/identify C. auris, these methods are time-consuming, expensive, and require expertise. Therefore, the objective of the present study was to assess the potential use of a novel chromogenic medium, CHROMagar™ Candida Plus, as an economical alternative to expensive and laborious diagnostic tests. We compared CHROMagar™ Candida Plus with the standard enrichment (salt Sabouraud Dulcitol broth) medium to test the recovery efficiency of C. auris from surveillance samples. We also tested CHROMagar™ Candida Plus for its ability to distinguish C. auris from other yeast species. One hundred surveillance samples were cultured on CHROMagar™ Candida Plus and Dulcitol broth and incubated at 37 °C and 40 °C, respectively. Additionally, 32 Candida and yeast species were cultured on CHROMagar™ Candida Plus at 37 °C for three days to rule out any close resemblance to C. auris. Of 100 surveillance samples tested, 69 yielded presumptive positive C. auris exhibiting creamy pink colonies with a blue halo on CHROMagar™ Candida Plus within three days of incubation, and MALDI-TOF MS confirmed all by day 4. On the other hand, 69 of 100 surveillance samples yielded turbidity in Dulcitol broth by days 3-14 with final MALDI identification by days 5 to 17. Both media failed to identify one sample each, resulting in assay sensitivity and specificity of 99% and 97%, respectively. Of Candida and yeast species tested, 75-80% of C. metapsilosis and C. orthospilosis were misidentified as C. auris. However, previous studies indicated that these species are rarely detected in surveillance screening of C. auris. Naganishia diffluens also resembled C. auris, although it required different temperature growth (30 °C). In conclusion, CHROMagar™ Candida Plus provides rapid presumptive identification of C. auris. It would be another valuable tool in surveillance efforts to control the spread of C. auris in healthcare.

Keywords: Candida auris; Chromogenic; MALDI-TOF MS; Surveillance.

Fig. 1

Workflow of surveillance sample testing using CHROMagar™ Candida Plus medium. A 50 µl of surveillance sample was inoculated on a CHROMagar™ Candida Plus plate and spread evenly using a disposable spreader. B 10 µl of surveillance sample was also inoculated on another CHROMagar™ Candida Plus plate and streaked with a 10 µl yellow plastic loop to obtain single colonies. Plates were incubated at 37 ˚C for 72 h and then imaged using a Canon EOS 80D Camera through Ortery Photosimile software and processed using Photoshop 22.4.2. Workflow template was created with BioRender.com

Fig. 2

Comparison of days required for final identification of C. auris using CHROMagar™ Candida Plus and Dulcitol broth. Presumptive identification on CHROMagar™ Candida Plus for all C. auris positive surveillance samples took 3 days followed by final identification by MALDI-TOF MS on the fourth day (orange bar). Final identification with Dulcitol broth and MALDI-TOF MS had a broad range from day 5 to day 17 (blue bars)