LETTER
Candida auris is an emerging public health threat. Since initial identification (1), it has become a global pathogen, causing outbreaks in various health care settings. Despite its capacity for health care-associated transmission, rapid, accurate identification remains challenging in clinical laboratories. This poses a public health threat, as early identification is crucial for initiating infection control measures in order to limit transmission and for guiding antifungal therapy, as most C. auris strains are resistant to one or more antifungal drugs.
Over 200 C. auris cases have been reported in the United States (2), though the worldwide burden of C. auris is largely unknown. As an emerging pathogen, C. auris may be mischaracterized and underreported due to unreliable identification in automated systems, as C. auris biochemical fingerprints have not yet been incorporated into many microbiology databases. In commercially available automated systems, C. auris has been misidentified as other Candida species, Rhodotorula glutinis, and Saccharomyces cerevisiae (3–10). RapID Yeast Plus (Remel, Thermo Fisher Scientific, Lenexa, KS) is a commercial, manual, biochemical enzyme-based system used in many clinical laboratories to identify medically important yeasts. RapID relies on several chromogenic reactions and the Electronic RapID Coded Compendium (ERIC) for organism identification. To date, C. auris isolation has not been validated by this system and is not included in the electronic coded compendium.
We obtained a reference panel of 10 C. auris isolates from the U.S. Centers for Disease Control and Prevention designed to assist clinical laboratories in the identification of this organism. The isolates were subcultured to Sabouraud dextrose agar (Emmons formulation; BD, Sparks, MD). Cultures used for inoculum preparation were incubated at 30°C for 48 h. Using a cotton swab, sufficient growth from the agar plate culture was suspended in RapID inoculation fluid (2 ml) to achieve the appropriate visual turbidity according to the manufacturer's package insert. The inoculum fluid was transferred into reaction cavities within the panel, which was incubated at 30°C in a non-CO2 incubator for 4 h. The preformulated reagents were added according to the manufacturer's instructions. Based on pH and chromogenic changes, a microcode, which was entered into the ERIC database for species identification with an associated probability, was assigned to each panel. Testing was performed in duplicate for each reference isolate. If disagreement occurred between the first two rounds of testing for any isolate, a third test was performed for adjudication.
Glucose utilization, the enzymatic hydrolysis of p-nitrophenyl-α-d-glucoside, and the hydrolysis of proline-β-naphthylamide were common to all C. auris reference isolates (Table 1). Nine isolates were misidentified as Candida parapsilosis, with satisfactory probability levels ranging from 95.68% to 99.9%. One isolate was misidentified as Candida tropicalis; however, the biofrequency value was questionable.
TABLE 1.
Biochemical analysis of reference Candida auris strains using RapIDa
| Lot no. | Remel RapID identification | Probability (%) | Probability level | Microcode | Presence of the following reactive ingredient: |
||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| Glu | Suc | Tre | αGlu | PHS | PCHO | PRO | |||||
| 1 | C. parapsilosis | 95.68 | Satisfactory | 102001 | + | − | − | + | − | − | + |
| 2 | C. parapsilosis | 99.9 | Implicit | 102031 | + | − | − | + | + | + | + |
| 3 | C. parapsilosis | 95.68 | Satisfactory | 102001 | + | − | − | + | − | + | + |
| 4 | C. parapsilosis | 95.68 | Satisfactory | 102001 | + | − | − | + | − | − | + |
| 5 | C. parapsilosis | 99.9 | Implicit | 102031 | + | − | − | + | + | + | + |
| 6 | C. parapsilosis | 95.68 | Satisfactory | 102001 | + | − | − | + | − | − | + |
| 7 | C. parapsilosis | 95.68 | Satisfactory | 102001 | + | − | − | + | − | − | + |
| 8 | C. tropicalisb | 99 | Questionable | 512001 | + | + | + | + | − | − | + |
| 9 | C. parapsilosis | 95.68 | Satisfactory | 102001 | + | − | − | + | − | − | + |
| 10 | C. parapsilosis | 95.68 | Satisfactory | 102001 | + | − | − | + | − | − | + |
The reference isolate for each lot was C. auris. Glu, glucose; Suc, Sucrose; Tre, Trehalose; αGlu, p-nitrophenyl-α-d-glucoside; PHS, p-nitrophenylphosphate; PCHO, p-nitrophenyl phosphorylcholine; Pro, proline-β-naphthylamide.
The biofrequency value was not within acceptable limits for reliable identification, and thus ERIC advised reisolation and repeat testing to ensure the purity of the sample.
We demonstrate that C. auris is generally misidentified as C. parapsilosis, using the RapID yeast identification system. Laboratories using the RapID system should be aware of the potential enzymatic profile patterns associated with C. auris and pursue additional testing to elicit species identification when C. parapsilosis is initially identified if pertinent to clinical care or if epidemiological criteria suggesting possible C. auris organisms (11) are present.
ACKNOWLEDGMENTS
We thank the CDC AR Isolate Bank for providing the C. auris reference strains used in this study. We thank Shawn Lockhart for his review of the manuscript.
We declare that we have no conflicts of interest to disclose.
REFERENCES
- 1.Satoh K, Makimura K, Hasumi Y, Nishiyama Y, Uchida K, Yamaguchi H. 2009. Candida auris sp. nov., a novel ascomycetous yeast isolated from the external ear canal of an inpatient in a Japanese hospital. Microbiol Immunol 53:41–44. doi: 10.1111/j.1348-0421.2008.00083.x. [DOI] [PubMed] [Google Scholar]
- 2.Centers for Disease Control and Prevention. 2018. Tracking Candida auris. Centers for Disease Control and Prevention, Atlanta, GA: https://www.cdc.gov/fungal/diseases/candidiasis/tracking-c-auris.html Accessed 1 February 2018. [Google Scholar]
- 3.Lockhart S, Etienne KA, Vallabhaneni S, Farooqi J, Chowdary A, Govender NP, Colombi AL, Calvo B, Cuomo CA, Desjardins CA, Berkow EL, Castanheira M, Magobo RE, Jabeen K, Ashgar RJ, Meis JF, Jackson B, Chiller T, Litvintseva AP. 2017. Simultaneous emergence of multidrug-resistant Candida auris on 3 continents confirmed by whole-genome sequencing and epidemiological analyses. Clin Infect Dis 64:134–140. doi: 10.1093/cid/ciw691. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 4.Al-Siyabi T, Al Busaidi I, Balkhair A, Al-Muharmi Z, Al-Salti M, Al'Adawi B. 2017. First report of Candida auris in Oman: clinical and microbiological description of five candidemia cases. J Infect 75:373–376. doi: 10.1016/j.jinf.2017.05.016. [DOI] [PubMed] [Google Scholar]
- 5.Chowdhary A, Anil Kumar V, Sharma C, Prakash A, Agarwal K, Babu R, Dinesh KR, Karim S, Singh SK, Hagen F, Meis JF. 2014. Multidrug-resistant endemic clonal strain of Candida auris in India. Eur J Clin Microbiol Infect Dis 33:919–926. doi: 10.1007/s10096-013-2027-1. [DOI] [PubMed] [Google Scholar]
- 6.Kathuria S, Singh PK, Sharma C, Prakash A, Masih A, Kumar A, Meis JF, Chowdwary A. 2015. Multidrug-resistant Candida auris misidentified as Candida haemulonii. J Clin Microbiol 53:1823–1830. doi: 10.1128/JCM.00367-15. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 7.Lee WG, Shin JH, Uh Y, Kang MG, Kim SH, Park KH, Jang HC. 2011. First three reported cases of nosocomial fungemia caused by Candida auris. J Clin Microbiol 49:3139–3142. doi: 10.1128/JCM.00319-11. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 8.Mizusawa M, Miller H, Green R, Lee R, Durante M, Perkins R, Hewitt C, Simner PJ, Carroll KC, Hayden RT, Zhang SX. 2017. Can multidrug-resistant Candida auris be reliably identified in clinical microbiology laboratories? J Clin Microbiol 55:638–640. doi: 10.1128/JCM.02202-16. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 9.Clancy CJ, Nguyen MH. 2017. Emergence of Candida auris: an international call to arms. Clin Infect Dis 64:141–143. doi: 10.1093/cid/ciw696. [DOI] [PubMed] [Google Scholar]
- 10.Spivak ES, Hanson KE. 2018. Candida auris: an emerging fungal pathogen. J Clin Microbiol 56:e01588-17. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 11.Lockhart SR, Jackson BR, Vallabhaneni S, Ostrosky-Zeichner L, Pappas PG, Chiller T. 2017. Thinking beyond the common Candida species: need for species-level identification of Candida due to the emergence of multidrug-resistant Candida auris. J Clin Microbiol 55:3324–3327. doi: 10.1128/JCM.01355-17. [DOI] [PMC free article] [PubMed] [Google Scholar]