Rapid, Accurate Identification of Candida auris by Using a Novel Matrix-Assisted Laser Desorption Ionization–Time of Flight Mass Spectrometry (MALDI-TOF MS) Database (Library)

Abstract

T he newly emerging multidrug-resistant yeast Candida auris can cause serious infections and may be underrepresented, as it can be misidentified as other species (e.g., Candida haemulonii, Candida duobushaemulonii, or Saccharomyces cerevisiae) by some biochemical-based testing systems (1-4). Candida auris can be identified using research use only (RUO) libraries on matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) platforms, such as the Biotyper platform (Bruker, Billerica, MA), but may need labor-intensive full-tube extraction procedures (3-5). Our laboratory uses the Biotyper equipped with both FDA-approved and RUO libraries. The RUO library contains three C. auris entries, but the identification of C. auris remains a challenge, and some isolates are never identified by the system. To improve the identification, a novel database, "CMdb," was developed and evaluated on our two Biotyper systems. The CMdb was created using internationally collected yeasts from the CDC (6) and one in-house clinical C. auris isolate. Bruker's protocol was used for database creation, and the direct on-plate extraction method was used for target preparation (7). The CMdb was evaluated on 23 clinical C. auris isolates, 20 CDC strains, 52 isolates of 10 other yeast species, and 28 isolates of 16 bacterial species.

Candida auris Clinical Isolates from South Korea: Identification, Antifungal Susceptibility, and Genotyping

“…In a study using the CDC panel of ten C. auris isolates, all ten C. auris isolates were identified correctly by the Vitek MS system after the direct extraction method, while 50% and 100% of C. auris isolates were correctly identified by the Biotyper after direct on-plate extraction and after full-tube extraction, respectively, indicating that the Biotyper performs better following the full-tube extraction method (8). Although direct on-plate FA extraction is simpler, Bruker Biotyper MS instructions recommend full-tube FA/ACN extraction for yeast identification (10,14). The reasons for the low rate of correct C. auris identification by Biotyper after direct on-plate extraction are poorly understood, but may be due to the characteristics of this pathogen, which renders solubilization of proteins difficult by simple extraction, or due to insufficient database entries to enable spectral matches because the C. auris database is designed for isolates after in-tube FA/ACN extraction.…”

Candida auris: epidemiological situation, laboratory capacity and preparedness in the European Union and European Economic Area*, January 2018 to May 2019

“…It has been detected on five continents within a few years of its first identification in 2009. Identification of C. auris requires specialised laboratory methodology such as matrix-assisted laser desorption/ionisation-time of flight (MALDI-TOF) mass spectrometry or sequencing of specific gene loci [2,3]. Reliance on traditional methods may lead to misidentification.…”

“…Species identification of C. auris can be challenging but is a prerequisite for adequate treatment and effective infection control measures [2,3,13]. Yet, seven EU/EEA countries still reported that a reference laboratory did not exist in their country.…”

External Quality Assessment Evaluating the Ability of Dutch Clinical Microbiological Laboratories to Identify Candida auris

“…Whole genome analysis suggests the emergence of five different C. auris clades [42,43]. It seems that by using reference databases containing more C. auris spectra from different clades, most isolates can be identified correctly with MALDI-TOF MS [44]. Thus, it is likely that with the currently updated Bruker MALDI Biotyper and bioMérieux Vitek MS reference libraries, that contain several C. auris spectra, excellent identification may be achieved.…”