Use of the Bruker MALDI Biotyper for Identification of Molds in the Clinical Mycology Laboratory

Abstract

Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) is increasingly used for the identification of bacteria and fungi in the diagnostic laboratory. We evaluated the mold database of Bruker Daltonik (Bremen, Germany), the Filamentous Fungi Library 1.0. First, we studied 83 phenotypically and molecularly well-characterized, nondermatophyte, nondematiaceous molds from a clinical strain collection. Using the manufacturer-recommended interpretation criteria, genus and species identification rates were 78.3% and 54.2%, respectively. Reducing the species cutoff from 2.0 to 1.7 significantly increased species identification to 71.1% without increasing misidentifications. In a subsequent prospective study, 200 consecutive clinical mold isolates were identified by the MALDI Biotyper and our conventional identification algorithm. Discrepancies were resolved by ribosomal DNA (rDNA) internal transcribed spacer region sequence analysis. For the MALDI Biotyper, genus and species identification rates were 83.5% and 79.0%, respectively, when using a species cutoff of 1.7. Not identified were 16.5% of the isolates. Concordant genus and species assignments of MALDI-TOF MS and the conventional identification algorithm were observed for 98.2% and 64.2% of the isolates, respectively. Four erroneous species assignments were observed using the MALDI Biotyper. The MALDI Biotyper seems highly reliable for the identification of molds when using the Filamentous Fungi Library 1.0 and a species cutoff of 1.7. However, expansion of the database is required to reduce the number of nonidentified isolates. Molds are an important cause of morbidity and mortality among hospitalized patients, particularly among those who are immunocompromised or suffer from serious underlying disease (1-3). Traditionally, identification of molds in the diagnostic mycology laboratory is based on phenotypic traits (4-6). Sufficient growth and sporulation are required to assess macromorphological criteria, including growth on different media and at different temperatures, as well as micromorphological criteria, such as shape of conidia, spores, and mycelial structures. Conventional identification methods have important drawbacks: (i) conventional identification of molds requires a comparably long time to result, (ii) the enormous morphological variability of molds asks for extensive individual expertise of the laboratory personnel, and (iii) some mold isolates do not develop their characteristic structural features under laboratory conditions, preventing identification or even leading to misidentifications. Nucleic acid sequence analysis of the internal transcribed spacer (ITS) regions between the 18S and 28S rRNA genes has emerged as an alternative to conventional identification, especially for isolates with unusual phenotypic profiles and rare molds, including environmental contaminants (4, 7-9).Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) is increasingly used in diagnostic bacter...

Molecular and Matrix-Assisted Laser Desorption Ionization–Time of Flight Mass Spectrometry-Based Characterization of Clinically Significant Melanized Fungi in India

“…This library represents the first commercial database of Bruker Daltonics for the identification of molds grown in liquid media. Interestingly, since 2011 only one study utilized liquid cultivation with ethanol-formic acid extraction for sample preparation for identification of filamentous fungi by a MALDI Biotyper (19). Although protein extraction from cultures grown on solid media simplifies preanalytical processes and reduces the identification time, nonetheless, in our experience excellent identification was observed with cultures grown in liquid media.…”

Evaluation of the Vitek MS Matrix-Assisted Laser Desorption Ionization–Time of Flight Mass Spectrometry System for Identification of Clinically Relevant Filamentous Fungi

“…For filamentous fungi, databases have been limited, and unlike bacteria, filamentous fungi require additional processing steps to disrupt the cell wall, extract proteins, and inactivate the isolate (10). These additional processing steps and limited libraries have led laboratories to develop their own methodologies and databases to overcome these barriers to adoption (11)(12)(13).…”

Matrix-Assisted Laser Desorption Ionization–Time of Flight (MALDI-TOF) Mass Spectrometry Using the Vitek MS System for Rapid and Accurate Identification of Dermatophytes on Solid Cultures

“…D ermatophytes in the genera Epidermophyton, Microsporum, and Trichophyton are usually characterized and identified by cultural and morphological characters and physiological tests or, more recently, by sequencing (1). Morphological identification is time-consuming and complex, usually requiring expert mycological knowledge, while sequencing is comparatively expensive and at least 2 to 3 days elapse before sequencing results are available.Matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry (MS) is a reliable technique for the identification and typing of microbial pathogens such as bacteria (2-7), yeasts (8-10), and filamentous fungi, including dermatophytes (7,(11)(12)(13)(14)(15)(16)(17). Recent studies confirm that this technique may be very attractive for dermatophyte identification (18-22).…”

“…Matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry (MS) is a reliable technique for the identification and typing of microbial pathogens such as bacteria (2-7), yeasts (8)(9)(10), and filamentous fungi, including dermatophytes (7,(11)(12)(13)(14)(15)(16)(17). Recent studies confirm that this technique may be very attractive for dermatophyte identification (18)(19)(20)(21)(22).…”