Abstract

Background: Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) is a powerful technique for the identification of microorganisms. The technique normally requires a sample preparation procedure before instrumental analysis, which can be somewhat labor-intensive when numbers of samples are large. The direct smear method, in which samples are directly smeared on the sample plates and subsequently subjected to instrumental analyses, can save time and is less labor-intensive. However, the method has rarely been tested on filamentous fungi, although it has been successfully used in the identification of bacteria and yeasts. In the present study, we examined the method using clinically-collected filamentous fungi.
Methods: Three hundred forty-eight isolates of filamentous fungi representing 9 species collected from body fluids of patients were analyzed on the VITEK MS version 3.0 system, a popular commercial MALDI-TOF MS system, using the direct smear method. For those misidentified or unidentified, the samples were retested. All fungal species were determined through DNA sequencing.
Results: Among 334 isolates that were included in the database of the VITEK system, 286 (85.6%) samples were correctly identified. After retesting, the rate of correct identification increased to 91.0%. Aspergillus fumigatus exhibited a 95.2% rate of correct identification before retesting, whereas Aspergillus niger showed the rate at only 46.5% (58.1% even with retesting).
Conclusions: The direct smear method could be used in the identification of filamentous fungi found in body fluids of patients by MALDI-TOF MS at good rates of correct identification. The method is simple and time-saving, and deserves further evaluation.

DOI: 10.7754/Clin.Lab.2022.221003