Background: Accurate species identification is of particular interest in the case of A. fumigatus complex given that sibling species show systematically low susceptibility to antifungal agents. MALDI-TOF could be a good alternative for the discrimination of A. fumigatus sensu stricto and cryptic species but information about this topic is limited.
Materials/methods: Morphologically identified A. fumigatus complex isolates (n=617) collected in a multicentre surveillance study conducted in Spain were further submitted to antifungal susceptibility testing. Resistant species were also molecularly identified by β-tubulin sequencing. All isolates, cultured on Sabouraud agar plates during 2-3 days, were identified by MALDI-TOF. Conidia were mechanically disrupted by vortexing for 5 min. The sample was centrifuged and the pellet was dried thoroughly and submitted to a standard protein extraction. 1µl of the supernatant was spotted on the MALDI target plate and covered with 1µl of matrix. All isolates were analysed in duplicates.
Results: MALDI-TOF accurately identified all A. fumigatus sensu stricto isolates (n=592) as such, showing score values ≥2.0 in 87.7% of them. The remainder isolates were identified as cryptic species (n=25); in 14/25 of them, identification was concordant with β-tubulin sequencing: A. lentulus (n=10), Neosartoria pseudofisheri (n=1) and N. udagawae (n=3) isolates. However, A. fumigatiaffinis (n=7) were consistently misidentified as A. lentulus (CBS 117267 strain) with score values ≥1.8; the remaining cryptic species isolates – A. novofumigatus (n=2) and N. tsurutae (n=2) – were also misidentified as N. pseudofisheri. The latter misidentifications could be detected since they were considered as unreliable reports due to their low scores and inconsistency through the top ten identifications provided by MALDI-TOF.
Conclusions: MALDI-TOF proved high reliability to discriminate between A. fumigatus sensu stricto and cryptic species within the A. fumigatus complex. Although the identification of cryptic species was poor (53.8%), particularly for non-A. lentulus species, the presence of cryptic species may be suspected by low scores and inconsistent results by MALDI-TOF. Inclusion in the databases and/or peak analysis may improve identification of cryptic species in the near future.
Presenter email address: [email protected]
Full conference title:
- ECCMID 30th (2020)