The similarities and differences of Aspergillus and Penicillium strains detected by MALDI-TOF mass spectrometry of the hyphal extracts

Natalya Vasilyeva*1, Igor Riabinin1, Yaroslava Jolya2, Anna-Mariya Volontsevicha2, Olga Shadrivova3

Author address: 

1 Kashkina Research Institute of Medical Mycology, North-Western State Medical University named after I.I. Mechnikov, Saint-Petersburg, Russian Federation, 2 faculty of clinical medicine, North-Western State Medical University named after I.I. Mechnikov, Saint-Petersburg, Russian Federation, 3 department of clinical mycology, immunology and allergy, North-Western State Medical University named after I.I. Mechnikov, Saint-Petersburg, Russian Federation

Abstract: 

Background: Penicilli are the closest related micromycetes of invasive aspergillosis causative agents. They have a different morphology, but similar mass-spectra (MS) of polypeptide metabolites, so that individual strains of penicilli can be misidentified as aspergilli by using MALDI-TOF-MS. The purpose is to compare the hyphal-extracts-MS of Aspergillus spp. and Penicillium spp. representatives to reveal similar groups of species of these fungi.

Materials/methods: MS of fungal culture extracts were obtained as described previously (Riabinin I.A. et al., 6th AAA, 2014). 70 MS from strains of 4 Penicillium species (P_digitatum, P_chrysogenum, P_camemberti, Penicillium sp. Terverticillata section) and 14 Aspergillus species (A_fumigatus, A_calidoustus, A_flavus, A_niger, A_tubingensis, A_tamarii, A_ochraceus, A_candidus, A_sydowii, A_versicolor, A_nidulans, A_clavatus, A_wentii, E_amstelodami) were extracted from MS-bank of Kashkina Research Institute (>700 MS of filamentous fungi) for comparison of micromycetes. Original strains were identified by morphology, using MALDI-TOF-MS, and by targeted DNA sequencing of the ITS and β-tubulin regions (CLSI MM18-A). Selected MS were compared by constructing of the complex-correlation-index-matrix in MALDI Biotyper OC 3.1 software.

Results: The CCI-matrix is shown in the figure. Penicillium spp. are generally the most similar to A_calidoustus by their physico-chemical properties, the similarity is less pronounced with A_versicolor, A_tamarii, E_amstelodami and single strains of A_flavus and A_terreus. MS-differences of Aspergillus spp. significantly well-marked than in the Penicillium spp. The groups of A_fumigatus, A_niger, A_flavus, A_terreus strains were represented by relatively homogeneous MS, and the strains of P_digitatum were the most heterogeneous. MS from A_flavus and related to them A_tamarii were very similar. A_wentii and A_candidus have the most specific MS, while A_niger and A_ochraceus have the least specific MS. The strains of P_digitatum have more coincidences in MS-composition with P_camemberti than with P_chrysogenum. The isolates of the species from which the protein-peptide-extract is easily obtained, A_fumigatus and A_terreus, turned out to be the closest to some species with rigid cell wall: A_niger and A_flavus, respectively. The correlation coefficient values confirming the found patterns were copied.

Conclusions: Our research has shown that the physico-chemical differences in the Trichocomaceae taxons are uneven, therefore a qualified microscopic examination of the microfungal isolate should always complement of MALDI-TOF-MS.