Development and validation of an extended database for yeast identification by MALDI-TOF MS in Argentina

Abstract

Matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS) has revolutionized the identification of microorganisms in clinical laboratories because it is rapid, relatively simple to use, accurate, and can be used for a wide number of microorganisms. Several studies have demonstrated the utility of this technique in the identification of yeasts; however, its performance is usually improved by the extension of the database. Here we developed an in-house database of 143 strains belonging to 42 yeast species in the MALDI Biotyper platform, and we validated the extended database with 388 regional strains and 15 reference strains belonging to 55 yeast species. We also performed an intra- and interlaboratory study to assess reproducibility and analyzed the use of the cutoff values of 1.700 and 2.000 to correctly identify at species level. The creation of an in-house database that extended the manufacturer's database was successful in view of no incorrect identification was introduced. The best performance was observed by using the extended database and a cutoff value of 1.700 with a sensitivity of .94 and specificity of .96. A reproducibility study showed utility to detect deviations and could be used for external quality control. The extended database was able to differentiate closely related species and it has potential in distinguishing the molecular genotypes of Cryptococcus neoformans and Cryptococcus gattii.

First case report of cryptococcosis due to Cryptococcus decagattii in a pediatric patient in Argentina

“…MALDI-TOF MS identification of the isolates showed the best match results with the MSP of the genotype VGIII strains. This is in agreement with previous studies demonstrating a high potential of this technique to correctly differentiate between the major genotypes 4 .…”

“…Urease, phenoloxidase, and canavanine-glycinebromothymol blue (CGB) tests were positive. Identification by MALDI-TOF MS was performed as described previously 4 . This technique identified both isolates as C. gattii s.l.…”

First Genome Sequences of Two Multidrug-Resistant Candida haemulonii var. vulnera Isolates From Pediatric Patients With Candidemia

“…The emergence of non-albicans species has reinforced the importance of improving microbiological laboratory procedures, in particular concerning the adoption of molecular methods to overcome the limitation of classical methods in the identification of these opportunistic microorganisms ( Lockhart et al, 2017a ). Although MALDI-TOF MS is fast and accurate for yeast identification, it shows variable performance in the discrimination of C. haemulonii complex isolates and related species ( Kathuria et al, 2015 ; Grenfell et al, 2016 ; Taverna et al, 2019 ). The two isolates reported here were identified as C. haemulonii sensu stricto using MALDI-TOF MS, while ITS1 and ITS2 analysis, obtained from the assembled genomes, identified the isolates as C. haemulonii var.…”

Identification and Antifungal Susceptibility Analysis of Stephanoascus ciferrii Complex Species Isolated From Patients With Chronic Suppurative Otitis Media

“…The lack of reference database for C. allociferrii and C. mucifera limits the ability of MALDI-TOF MS in identification, making it essential to construct the reference database of S. ciferrii complex species. Taverna et al (2019) developed an in-house database of 143 strains belonging to 42 yeast species in the MALDI Biotyper platform, making it possible to differentiate closely related species and distinguish the molecular genotypes of Cryptococcus neoformans and Cryptococcus gattii . Moreover, Veloo et al (2018) optimized the identification of clinical anaerobic isolates with MALDI-TOF MS using 6,309 anaerobic isolates, thus increasing the number of anaerobic isolates that could be identified with high confidence.…”