Performance and Cost Analysis of Matrix-Assisted Laser Desorption Ionization–Time of Flight Mass Spectrometry for Routine Identification of Yeast

Abstract

Matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry was compared to phenotypic testing for yeast identification. MALDI-TOF mass spectrometry yielded 96.3% and 84.5% accurate species level identifications (spectral scores, >1.8) for 138 common and 103 archived strains of yeast. MALDI-TOF mass spectrometry is accurate, rapid (5.1 min of hands-on time/identification), and cost-effective ($0.50/sample) for yeast identification in the clinical laboratory.Candida is the fourth leading cause of nosocomial bloodstream infections in the United States (22). Candida albicans is the major species causing morbidity and mortality, but other, less common opportunistic yeasts, including non-albicans Candida, Cryptococcus, Pichia, Rhodotorula, Trichosporon, and Saccharomyces species have also been seen in immunocompromised settings (4,15,31). Accurate and rapid identification of yeasts is critical for treatment due to species-specific susceptibility patterns. Phenotypic identification can be timeand labor-intensive and can at times yield erroneous identifications (6,20,24,30). Rapid latex agglutination assays are available, but for only a limited number of species (12, 23). Molecular assays are often accurate but can be expensive and complex.Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) has recently been described as a rapid, reliable, and cost-effective alternative for bacterial, mycobacterial, and fungal identification (1,10,19,21,27,29). The technique relies on the generation of microorganism "protein fingerprints" that are compared to reference spectra in a well-characterized library (9).In this study, we assessed the performance of the MALDI Biotyper 2.0 Microflex LT spectrometer (Bruker Daltonics, Inc., Billerica, MA) for the identification of common and uncommon yeasts (n ϭ 261). A 1-month, blinded, prospective study included 145 freshly collected yeast isolates encountered in the routine laboratory workflow on various selective fungal isolation media, including Mycosel agar, brain heart infusion (BHI), Sabouraud's (SAB) agar, and inhibitory mold agar (IMA) (Becton Dickinson, Sparks, MD) (17). C. albicans was identified by germ tube formation, and Candida glabrata was identified by the rapid-assimilation-of-trehalose (RAT) test (17). Both tests have inherent limitations, including false-positive germ tube formation by non-albicans species (e.g., Candida dubliniensis) and the need to carefully control the inoculum size (11, 16). Round, variably-sized yeasts resemblingCryptococcus were identified at the species level using urea and pigment production methods, as described previously (14). All other yeasts were identified using the API 20C AUX yeast identification system (bioMérieux, Hazelwood, MO) and microscopic morphology on cornmeal agar with Tween 80 (17). Additionally, 116 strains (IMA subcultures at 30°C) from an archived collection of less common yeasts that were previously identified using API 20C and D2 sequencing were identified usi...

Study on the effects of near-future ocean acidification on marine yeasts: a microcosm approach

“…Yet, direct identification of environmental yeast isolates by MALDI-TOF MS is still limited. As identification successes obtained for clinical yeast isolates are very promising (Marklein et al 2009;Stevenson et al 2010;van Veen et al 2010;Dhiman et al 2011), an expansion of the database toward environmental isolates is desirable. With these data becoming available, it will be possible to fully exploit the capacity of this rapid and costeffective method for environmental studies.…”

“…Furthermore, reference spectra created from measurements of one isolate can be compared with those of other isolates to analyze phylogenetic relationships and thus classify unknown organisms. This mass spectrometric technique has been extensively applied to the study of clinically important yeasts, yielding high rates of correct species-level identifications (e.g., Marklein et al 2009;Stevenson et al 2010;van Veen et al 2010;Dhiman et al 2011). Yet, to our knowledge, it has not been applied to yeasts in the context of ecological studies.…”

Advantages of Using Matrix-Assisted Laser Desorption Ionization–Time of Flight Mass Spectrometry as a Rapid Diagnostic Tool for Identification of Yeasts and Mycobacteria in the Clinical Microbiological Laboratory

“…The use of matrixassisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) for the rapid identification of clinical yeast and mycobacterial isolates has been evaluated in some studies (13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25). However, there has been a limited number of direct comparison studies focusing on the performance of the two MALDI-TOF systems to rapidly identify yeast and mycobacterial clinical isolates (26)(27)(28).…”

Identification of Uncommon Clinically Important Yeasts and Moulds by the Bruker Biotyper Matrix-Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry (MALDI-TOF MS) System in a Global Antifungal Surveillance Program

“…7 organism collection. It should be noted that whereas the confidence scores of ≥2.0 used for secure species level ID in the present study are those recommended by the manufacturer, other investigators have suggested that this breakpoint may be overly conservative and that lowering the secure species threshold to 1.8 improved species level ID of yeasts from 87%-92% to >99% of isolates while preserving 100% accuracy of IDs (Buchan and Ledeboer, 2013;Dhiman et al, 2011;Stevenson et al, 2010). In another study VanHerendael et al (2012) found that 100% of isolates with lower confidence scores indicating genus only ID were also correctly IDed to species level.…”