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

Abstract

bInvasive fungal infections have a high rate of morbidity and mortality, and accurate identification is necessary to guide appropriate antifungal therapy. With the increasing incidence of invasive disease attributed to filamentous fungi, rapid and accurate species-level identification of these pathogens is necessary. Traditional methods for identification of filamentous fungi can be slow and may lack resolution. Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) has emerged as a rapid and accurate method for identification of bacteria and yeasts, but a paucity of data exists on the performance characteristics of this method for identification of filamentous fungi. The objective of our study was to evaluate the accuracy of the Vitek MS for mold identification. A total of 319 mold isolates representing 43 genera recovered from clinical specimens were evaluated. Of these isolates, 213 (66.8%) were correctly identified using the Vitek MS Knowledge Base, version 3.0 database. When a modified SARAMIS (Spectral Archive and Microbial Identification System) database was used to augment the version 3.0 Knowledge Base, 245 (76.8%) isolates were correctly identified. Unidentified isolates were subcultured for repeat testing; 71/ 319 (22.3%) remained unidentified. Of the unidentified isolates, 69 were not in the database. Only 3 (0.9%) isolates were misidentified by MALDI-TOF MS (including Aspergillus amoenus [n ‫؍‬ 2] and Aspergillus calidoustus [n ‫؍‬ 1]) although 10 (3.1%) of the original phenotypic identifications were not correct. In addition, this methodology was able to accurately identify 133/144 (93.6%) Aspergillus sp. isolates to the species level. MALDI-TOF MS has the potential to expedite mold identification, and misidentifications are rare. Filamentous fungi are ubiquitous environmental microorganisms that have become increasingly important pathogens, especially in immunocompromised patients. Invasive fungal diseases have a high rate of morbidity and mortality, and accurate identification is necessary to guide appropriate antifungal therapy. Traditionally, the identification of filamentous fungi has required the use of different phenotypic methods in conjunction with macro-and microscopic assessment of the organism (1). This process requires highly trained mycologists, and, in some cases, turnaround time may be prolonged due to a requirement for extended incubation periods, potentially delaying appropriate therapy. Molecular methods, which can provide accurate identification to the species level, can be expensive, require specialized equipment or expertise, and are not commonly available in clinical laboratories.Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) has been utilized in the clinical microbiology laboratory for rapid and accurate identification of bacteria, mycobacteria, and yeasts (2-9). For filamentous fungi, databases have been limited, and unlike bacteria, filamentous fungi require additional processing steps to dis...

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“…To establish the utility of MALDI‐TOF MS in clinical scenarios, a series of studies were conducted on clinical isolates from patients . In these studies, known fungal species including genera other than Aspergillus were used to construct databases, and clinical isolates were compared against these databases for classification.…”

“…To unambiguously assign and verify species, designations were generally accomplished by performing DNA sequencing on a combination of: (i) β‐tubulin, (ii) calmodulin, (iii) actin, and (iv) the internal transcribed spacers, ITS1 and ITS2, that flank the 5.8S ribosomal DNA (ITS1–5.8S–ITS2). MALDI‐TOF MS could consistently predict the fungal species from patient‐derived isolates, if a reference spectrum was available …”

“…MALDI could identify common Aspergillus species more frequently than the rarer ones. However, when reference spectra from rarer species was included, MALDI‐TOF MS was better able to characterize species . In the past few years, numerous multihospital studies in several countries have shown the clinical application of this technology and the potential for standardization.…”

“…To establish the utility of MALDI-TOF MS in clinical scenarios, a series of studies were conducted on clinical isolates from patients. [131][132][133][134][135][136][137][138][139][140] In these studies, known fungal species including genera other than Aspergillus were used to construct databases, and clinical isolates were compared against these databases for classification. To unambiguously assign and verify species, designations were generally accomplished by performing DNA sequencing on a combination of: (i) β-tubulin, (ii) calmodulin, (iii) actin, and (iv) the internal transcribed spacers, ITS1 and ITS2, that flank the 5.8S ribosomal DNA (ITS1-5.8S-ITS2).…”

Identification of Molds by Matrix-Assisted Laser Desorption Ionization–Time of Flight Mass Spectrometry

“…This suggests that low spectrum quality rather than low database coverage could potentially explain the low scores (Ͻ2.0), although further studies are necessary to clarify these issues. In a very large evaluation study, 319 mold isolates from 43 different genera, recovered from different clinical specimens, were analyzed by using an updated Vitek MS database, the Vitek MS version 3.0 library, which contains unique species from 31 different genera of filamentous fungi (20 (20).…”