Background: Schizophyllum is an important genus of basidiomycetes that, apart from being of genetic and biotechnological interest, is reported as an opportunistic pathogen in mammals. In immunocompromised patients in particular, it can colonize and infect many sites, although it has mainly been found in the respiratory tract. Schizophyllum commune is the best-known species and the only one reported in a clinical setting. The aim of this study was to carry out a multi-locus phylogenetic analysis of 23 clinical isolates of Schizophyllum spp. that have been received from different hospitals in the USA and 9 reference strains held in different culture collections (six strains of S. commune and three representatives each one of S. radiatum, S. fasciatum and S. umbrinum), which will then determine the spectrum of species of that genus linked to human clinical specimens.
Material/methods: The clinical isolates were provided by the Fungus Testing Laboratory at the University of Texas Health Science Center (USA). The strains were cultivated on potato dextrose agar and the DNA was extracted after 7 to 10 days using the FastDNA® Kit and the FastPrep® Instrument. A PCR was performed to amplify the region of interest. The markers used for the study were the internal transcribed spacer (ITS) and the nuclear large subunit rDNA (LSU), using the ITS5 and LR5 primers, RNA polymerase II second largest subunit (RPB2), using 5F and 7CR primers, and translation elongation factor 1-alpha (EF-1α), using EF-983F and EF-2218R primers. PCR products were sequenced in both directions using the same primers at Macrogen Europe. Sequences were edited and assembled using Sequencher 4.1.4. The phylogenetic analyses were carried out by the Maximum Likelihood and Bayesian methods using MEGA v.6 and MrBayes v.3.1.2 software, respectively.
Results: The final tree, which comprised 2629 bp, revealed that 22 of the 23 clinical isolates from the USA were placed in the S. radiatum clade, with high support values, and only one isolate in the S. commune clade. This was an interesting result because it is the first time that this species has been reported in clinical samples. The two mentioned species show very similar morphological features in vitro (i.e, white, cottony, unsporulated colonies composed of hyphae with clamp connections). The rDNA region proved to be little variable and not phylogenetically informative in these fungi. The other markers studied showed a higher variance, enabling a better resolution.
Conclusions: Instead of S. commune, as commonly thought, S. radiatum was the prevalent species of the genus in clinical specimens from the USA.