Fungi belonging to Aspergillus section Flavi are of great economic importance due to their ability to produce carcinogenic mycotoxins. They may also be responsible for invasive aspergillosis in humans and animals. The high number of species with section Flavi and their morphological similarity make it difficult to ascertain their clinical and epidemiological particularities. In this study we present molecular characterization and azole susceptibility of clinical isolates belonging to section Flavi and collected from patients in two French hospitals.
Eighty-two isolates were included in the study. These clinical isolates were recovered from different specimens (essentially respiratory specimens) over a 15-year period (2001-2015) and stored frozen. The isolates were initially identified as members of Aspergillus section Flavi by morphological characteristics. After subculture, each isolate was identified to the species level by sequencing a part of the β-tubulin and calmodulin genes. The isolates were also screened for their susceptibility to itraconazole and voriconazole.
Among the 82 isolates, molecular analysis of the partial β-tubulin and calmodulin sequences showed that 80 isolates were A. flavus and 2 isolates were A. parasiticus and A. tamarii, respectively. These 2 isolates were isolated from sputa and were not resistant to azoles. Among A. flavus isolates, a limited polymorphism was observed for the partial β-tubulin gene: for 75 isolates (91%), sequences were identical to the reference sequence (A. flavus isolate NRRL 1957 beta-tubulin gene, partial cds, ACCESSION EF661485). For partial calmodulin gene, several polymorphisms were observed with only 14 sequences (17%) identical to the reference sequence (A. flavus isolate NRRL 1957 calmodulin gene, partial cds, ACCESSION EF661508). Two A. flavus isolates were resistant to voriconazole but not to itraconazole. Analysis of CYP51A gene polymorphism for these isolates is in progress.
For the first time in France, we molecularly characterized a large collection of clinical isolates belonging to Aspergillus section Flavi. Most of the isolates were identified as A. flavus and were susceptible to azole antifungal drugs. Nevertheless, the occurrence of a few resistant isolates highlights the importance of antifungal susceptibility testing.