Identifying indoor air Penicillium species: a challenge for allergic patients

Penicillium is the most common mould isolated in housing. Penicillium chrysogenum is the only species tested by prick test or serology for allergic patients. The American Institute of Medicine has accepted Penicillium as an aetiological agent of rhinitis in children and adults and as an asthma agent in children. However, few studies have identified Penicillium in housing to the species level (354 species). Phenotypic identification is difficult. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) should be an alternative. The aim of this study was (1) to identify the Penicillium species present in dwellings in Eastern France and (2) to evaluate the reliability of MALDI-TOF MS for identification, by comparing it to DNA sequencing and phenotypic identification.

Identification to the species level was performed by MALDI-TOF MS on 275 strains isolated from 48 dwellings. These results were compared to beta-tubulin gene sequencing and to the phenotypic aspects.

Thanks to MALDI-TOF, 235/275 strains could be identified (85.5 %). Fourteen species were identified among 23 Penicillium species included in the Filamentous Fungi Library 1.0 (Bruker Daltonics). However, 72.2  % of the strains belonged to five main taxa: P. chrysogenum (27.3 %), Penicillium glabrum (22.9 %), Penicilliumcommune (11.3 %), Penicillium brevicompactum (6.5 %) and Penicillium expansum (4.2 %).

Complete coherence between MALDI-TOF MS and sequence-based identification was found for P. chrysogenum, P. expansum, P. glabrum, Penicillium italicum and Penicillium corylophilum. The main drawback was observed for Penicillium crustosum, which included 21 strains (7.6 %) that could not be identified using MALDI-TOF MS.