Comparison of the Bruker Biotyper and VITEK MS Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry Systems Using a Formic Acid Extraction Method to Identify Common and Uncommon Yeast Isolates

Abstract

BackgroundMatrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) allows rapid and accurate identification of clinical yeast isolates. In-tube formic acid/acetonitrile (FA/ACN) extraction is recommended prior to the analysis with MALDI Biotyper, but the direct on-plate FA extraction is simpler. We compared the Biotyper with the VITEK MS for the identification of various clinically relevant yeast species, focusing on the use of the FA extraction method.MethodsWe analyzed 309 clinical isolates of 42 yeast species (four common Candida species, Cryptococcus neoformans, and 37 uncommon yeast species) using the Biotyper and VITEK MS systems. FA extraction was used initially for all isolates. If ‘no identification' result was obtained following the initial FA extraction, these samples were then retested by using FA (both systems, additive FA) or FA/ACN (Biotyper only, additive FA/ACN) extraction. These results were compared with those obtained by sequence-based identification.ResultsBoth systems correctly identified all 158 isolates of the four common Candida species after the initial FA extraction. The Biotyper correctly identified 8.7%, 30.4%, and 100% of 23 C. neoformans isolates after performing initial FA, additive FA, and FA/ACN extractions, respectively, while VITEK MS identified all C. neoformans isolates after the initial FA extraction. Both systems had comparable identification rates of 37 uncommon yeast species (128 isolates), following the initial FA (Biotyper, 74.2%; VITEK MS, 73.4%) or additive FA (Biotyper, 82.0%; VITEK MS, 73.4%).ConclusionsThe identification rate of most common and uncommon yeast isolates is comparable between simple FA extraction/Biotyper method and VITEK MS methods, but FA/ACN extraction is necessary for C. neoformans identification by Biotyper.

Performance of Microflex LT Biotyper and VITEK MS for Routine Identification of Yeasts

“…With the on-plate method, 95.7% of the isolates were correctly identified at the species level. With the in-tube extraction method, all isolates were correctly identified at the species level, consistent with previous reports [ 5 , 6 , 7 , 8 ]. The difference could be attributed to the ineffective lysis of the encapsulated yeast by the incomplete on-plate extraction method [ 9 ].…”

“…Yeasts were identified at isolation by conventional phenotypic methods, including the VITEK 2 YST card (bioMerieux, Durham, NC, USA). For the Biotyper analysis, on-plate formic acid extraction and in-tube formic acid/acetonitrile extraction were performed as previously described [ 5 ]. For the VITEK MS, only on-plate formic acid extraction was performed because the in-tube method is not recommended by the manufacturer.…”

“…Previous studies have suggested various cut-off values <2 [ 3 10 ], and we found that the laboratory-validated cut-off value yielded a higher identification rate without compromising accuracy. Lee et al [ 5 ] reported correct identification rates of 91.4% and 97.8% using the Biotyper (≥1.7) and the VITEK MS, respectively, with the on-plate method. Their results included 37 uncommon yeast species, which might explain why their correct identification rates were slightly lower than ours (94.7% and 99.5%).…”

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.…”

“…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. The identification of Candida species by MALDI-TOF systems depends on the database, the age or growth phase of the culture, and the extraction methods used in sample preparation (8,10,14). RUO libraries of two MALDI-TOF systems, Biotyper and .…”