[Investigation of the Antifungal Susceptibility and Virulence Factors of Fusarium Strains Isolated from Clinical Samples].

Abstract

Fusarium species are filamentous fungi which can cause various invasive and non-invasive conditions in humans, most notably keratitis and onychomycosis. Fusarium genus is divided into species complexes (SC), which are further separated into species. It is recommended to use molecular methods for species complex/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 to investigate their susceptibility to frequently used antifungals and some virulence factors. In our study, Fusarium strains obtained from clinical specimens in the Aydın Adnan Menderes University Hospital Medical Microbiology Laboratory between 2017 and 2022 were identified to the species complex level using internal transcribed spacer sequencing analysis. The susceptibility tests of the strains to amphotericin B, voriconazole and posaconazole were performed by standard broth microdilution method according to the recommendations of the European Committee on Antimicrobial Susceptibility Testing. Protease, phospholipase, esterase activities and biofilm forming abilities of Fusarium strains were investigated by phenotypic tests. It was investigated whether there was a statistical relationship between the minimum inhibitory concentration (MIC) values determined for species complexes, virulence factors and antifungals.Of the 22 Fusarium strains, 10 were identified as Fusarium solani species complex, six as Fusarium fujikuroi SC, five as Fusarium oxysporum SC, and one as Fusarium incarnatum-equiseti SC. The MIC90 values of the strains were determined as 16 µg/mL for amphotericin B, > 32 µg/mL for voriconazole and > 32 µg/mL for posaconazole with the antifungal susceptibility test. Posaconazole MIC values in F.oxysporum SC strains were significantly lower than others. Seven (32%) Fusarium strains had positive protease, 21 (95%) had positive esterase, 13 (59%) had positive phospholipase and 12 (55%) had positive biofilm test. F.solani SC strains have significant higher biofilm formation rate compared to F.oxysporum SC and F.fujikuroi SC strains. However, no significant difference was found between species for other virulence factors. In our study, no statistically significant correlation was found between amphotericin B, voriconazole, posaconazole MIC values of Fusarium strains and protease, phospholipase and esterase enzyme activities. As a result,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.