Abstract
Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) has emerged as a powerful microorganism identification tool. Research on MALDI-TOF MS identification of rare filamentous fungi is still lacking. This study aimed to evaluate the performance of MALDI-TOF MS in the identification of Scedosporium, Acremonium-like, Scopulariopsis, and Microascus species. Sabouraud broth cultivation and formic acid/acetonitrile protein extraction were used for MALDI-TOF MS identification by a Bruker Biotyper system. An in-house database containing 29 isolates of Scedosporium, Acremonium-like, Scopulariopsis, and Microascus spp. was constructed. A total of 52 clinical isolates were identified using the Bruker Filamentous Fungi Library v1.0 (FFL v1.0) alone, and Filamentous Fungi Library v1.0 plus the in-house library, respectively. The mass spectrum profile (MSP) dendrograms of the 28 Scedosporium isolates, 26 Acremonium-like isolates, and 27 Scopulariopsis and Microascus isolates were constructed by MALDI Biotyper OC 4.0 software, respectively. The correct species identification rate significantly improved when using the combined databases compared with that when using FFL v1.0 alone (Scedosporium spp., 75% versus 0%; Acremonium-like spp., 100% versus 0%; Scopulariopsis and Microascus spp., 100% versus 62.5%). The MSP dendrograms differentiated Acremonium-like species, Scopulariopsis and Microascus species clearly, but cannot distinguish species in the Scedosporium apiospermum complex. In conclusion, with an expanded database, MALDI-TOF MS is an effective tool for the identification of Scedosporium, Acremonium-like, Scopulariopsis, and Microascus species.
Highlights
In recent years, with the development of organ transplantation and the widespread use of immunosuppressants and antibiotics, the number of cases of invasive infections caused by filamentous fungi have increased (Brown et al, 2012)
Using FFL v1.0 alone, 60% (12/20) of Scedosporium isolates were identified with scores ≥ 2.0, while all of them were identified as Scedosporium apiospermum [anamorph] Pseudallescheria boydii [teleomorph], which was the only Scedosporium species represented in FFL v1.0, so clear species identification was not available
Our study indicated that MALDI-TOF MS is a powerful technique for rapid and accurate identification of the above species when using the Bruker database complimented with an in-house database and liquid culture
Summary
With the development of organ transplantation and the widespread use of immunosuppressants and antibiotics, the number of cases of invasive infections caused by filamentous fungi have increased (Brown et al, 2012). Scedosporium, Acremonium-like, Scopulariopsis, and Microascus spp. are saprobic fungi commonly found in the environment, some species have been reported as pathogens of humans, and most are opportunistic (RamirezGarcia et al, 2018; Perez-Cantero and Guarro, 2020a,b). Aremonium-like spp. comprise a high diversity of morphologically and genetically related fungi, among which Aremonium egyptiacum and Sarocladium kiliense are the most commonly involved in human diseases (PerezCantero and Guarro, 2020b). Scopulariopsis-like spp. include a group of hyaline and dematiaceous fungi, and most of the clinically relevant species belong to the genera Scopulariopsis and Microascus (Perez-Cantero and Guarro, 2020a). Due to the taxonomic complexity of these genera and the interspecies morphological similarities, morphological methods are often unable to identify these fungi at the species level (Perdomo et al, 2011; RamirezGarcia et al, 2018; Perez-Cantero and Guarro, 2020a). DNA sequencing allows accurate identification but is expensive, labor intensive, time consuming, and not suitable for routine laboratory testing
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