Investigation of the antifungal sensitivity and virulance factors of Fusarium strains isolated from clinical samples

Fusarium species are filamentous fungi that are widespread in nature and can cause various invasive and non-invasive conditions in humans, most notably keratitis and onychomycosis. Fusarium genus is divided into species complexes, which are further separated into species. It is recommended to use molecular methods for species identification due to the difficulties of morphological species diagnosis. Identification of Fusarium strains is crucial since antifungal susceptibility and virulence factors are likely to vary between species. In the present study, it was aimed to identify Fusarium strains by molecular methods, and investigate their susceptibility to frequently used antifungals and some virulence factors. Fusarium strains obtained from clinical specimens in the Aydın Adnan Menderes University Hospital Medical Microbiology Laboratory between 2017 and 2022 were identified at the species complex level using ITS sequencing analysis. The susceptibility tests of the strains to Amphotericin B, voriconazole and posaconazole were performed by broth microdilution method. Protease, phospholipase, esterase activities and biofilm forming abilities of Fusarium strains were investigated by phenotypic tests. The relationship between species complexes, the minimum inhibitory concentration (MIC) values to antifungals and virulence factors was investigated. Of the 22 Fusarium strains isolated 10 were identified as F. solani species complex, six as F. fujikuroi species complex, five as F. oxysporum species complex, and one as F. incarnatum-equiseti species complex. The MIC90 values of the strains were determined as 16 µg/ml for amphotericin B and >32 µg/ml for voriconazole and Posaconazole with the antifungal susceptibility test. Posaconazole MIC values in Fusarium oxysporum species complex strains were significantly lower than other species complex strains. Seven (32%) Fusarium strains had positive protease, 21 (95%) had positive esterase, 13 (59%) had positive phospholipase and 12 (55%) had positive biofilm test. Fusarium solani species complex strains have significant higher biofilm formation rate compared to F. oxysporum species complex and F. fujikuroi species complex strains. However, no significant difference was found between species for other virulence factors. In our study, no statistically significant correlation was found between the MIC values determined for amphotericin B, voriconazole and posaconazole of Fusarium strains and protease, phospholipase and esterase enzymes. It was concluded that the use of molecular methods is necessary for the identification of Fusarium species, and more comprehensive studies on the virulence factors and antifungal susceptibility of Fusarium species are needed. Key words: Fusarium, sequence analysis, protease, esterase, phospholipase, biofilm, antifungal susceptibility.