Implementation of MALDI-TOF Mass Spectrometry to Identify Fungi From the Indoor Environment as an Added Value to the Classical Morphology-Based Identification Tool

Abstract

IntroductionDuring the last decades, molds in the indoor environment have raised concern regarding their potential adverse health effects. The genera Aspergillus, Cladosporium, Penicillium, Alternaria, and yeasts, the most common fungi found indoors, include species with high allergenic and toxigenic potentials. Identification of these molds is generally performed by microscopy. This method has, however, some limitations as it requires mycologists with high expertise while identification is often limited to the genus level. Therefore, it is necessary to seek for fast and accurate tools, such as Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDITOF MS), enabling an identification to the species level and guiding general practitioners in their search for the underlying cause of a health problem.MethodsIn this study, 149 fungal air and dust isolates from 43 dwellings in Brussels were taken in collaboration with Brussels Environment RCIB/CRIPI and identified by both microscopy and MALDI-TOF MS in Sciensano's Indoor Mycology laboratory. Spectra obtained via MALDI-TOF MS were compared with data available in an in-house created reference database containing over 1,700 strains from the BCCM/IHEM fungal collection.ResultsA total of 149 isolates including 18 yeasts and 131 filamentous fungi were analyzed. Microscopic analysis indicated 18 yeast species and allowed identification of 79 isolates (53%) to the genus level. Only 36 isolates (24%) could be identified to the species complex level. Fifteen molds (10%) could not be identified, and one was indicated as sterile mycelia. No isolate was identified to species level. MALDI-TOF MS analysis identified 137 (92%) of the 149 isolates with a logscore > 1.7. Of these 137 isolates, 129 (87%) were identified to the species level (logscore > 2.0). For only 8 isolates (5%), identification was limited to the genus/section level (1.7 < logscore <2.0), and 12 isolates (8%) could not be identified.ConclusionA comparison of results obtained with both methods indicates an increased precision in identifications with MALDI-TOF MS analysis for 92% of the isolates, emphasizing its highly added value to the standard microscopic analysis in routine practice. In addition, MALDI-TOF MS also enables to assess the accuracy of microscopic identifications.

A Case of Invasive Fungal Infection Due to Scedosporium apiospermum in a Patient with Psoriasis

“…Although the RNA sequencing here were applied as supporting tool to avoid the low MALDI-TOF MS score, it might not be an ideal choice due to the disadvantages (expensive, time-consuming and prone to environmental contamination). By the MALDI-TOF MS, the isolate was identified to be S. apiospermum with a score of 1.788, which is acceptable for the filamentous fungi identification as reported by Motteu et al 25 Since MALDI-TOF MS offers the advantage of being fast, easy to perform and costeffective, we recommend that MALDI-TOF MS might be an appropriate option for the rapid identification of this pathogen if conditions permit.…”

A comprehensive review of microbial contamination in the indoor environment: sources, sampling, health risks, and mitigation strategies

“…Identification is made using an algorithm-based approach from databases containing the MS reference spectra of peptides and proteins extracted from known microorganisms (87, 88). This technique is gaining popularity for identifying bacteria and fungi from indoor dust and air samples (89)(90)(91). The microbial culture is transferred directly onto the sample target from the culture medium.…”

Spectroscopic analysis of mushrooms by surface-enhanced Raman scattering (SERS)

“…In fact, it is structured in several layers, with the innermost layer consisting of a covalently bound β-(1,3) glucan core and branched chitin [57,58]. The outer layers, in contrast, are more heterogeneous and adapted to the physiology of particular fungi and generally composed of polysaccharides such as β- (1,6) glucan, mannan, galactomannan, and also highly mannosylated glycoproteins [59]. In addition, pigments such as melanin are found in this outer layer, as was detected in the SERS of Pco.…”

“…In recent years, vibrational spectroscopy techniques allow a range of qualitative or quantitative information to be obtained, representing a new frontier for fungal identification [6], as well as Fourier transform infrared spectroscopy (FT-IR) and FT-Raman techniques have been successfully applied to identify different fungal species (Boletus spp., Ganoderma spp., Agaricus bisporus (J.E. Lange) Imbach, Mucor rouxii (Calmette) Wehmer and Mortierella sp.)…”