In vitro Antifungal Susceptibility Testing of Clinical and Environmental Fusarium Isolates in Iran

Background: Members of the genus Fusarium are common soil saprophytes and important plant pathogens which also cause a wide spectrum of diseases ranging from onychomycosis to the life - threatening systemic infections. The antifungal susceptibility patterns of Fusarium isolates varies in different species. Objectives: This study was undertaken to investigate the antifungal susceptibility pattern of environmental and clinical Fusarium isolates to conventionally - used azole antifungal drugs in Iran. Methods: A total of 36 Fusarium isolates (16 clinical and 20 environmental) were included in this study. All environmental isolates were obtained from the culture collection of medical mycology laboratory of the School of Public Health at Tehran University of Medical Sciences, Tehran, Iran. Clinical isolates were obtained from patients with onychomycosis and were identified by PCR - sequencing of a fragment of translation elongation factor 1 alpha gene. All clinical and environmental isolates were tested for their in vitro susceptibility to itraconazole (ITC) and voriconazole (VRC) according to the CLSI M38 - A2 standard. Statistical analysis of data was performed using SPSS version 21. Results: The majority of clinical isolates were identified as F. proliferatum (N = 6) followed by F. oxysporum (N = 4), F. solani (N = 3), F. verticillioides (N = 1), F. acutatum (N = 1), and F. thapsinum (N = 1). The lowest minimum inhibitory concentration (MIC) values of ITC was observed for environmental F. verticillioides isolates (N = 5, GM = 13.93 µg/mL). For VRC, the lowest MICs were recorded for environmental F. verticillioides isolates (N = 5, GM = 2.3 µg/mL), and the highest MICs were observed for clinical F. solani isolates (N = 3, GM = 10.08 µg/mL). ITC was inactive against all clinical and the majority of environmental Fusarium isolates (MICs ≥ 16 µg/mL). Significant differences were observed between MICs of ITC and VRC against environmental F. proliferatum and F. verticillioides isolates (P < 0.001 for both). Similarly, the susceptibility of clinical F. proliferatum, F. oxysporum and F. solani isolates to VRC was significantly different (P = 0.023). Conclusions: The resistance pattern in Fusarium isolates is species specific and, therefore, identification at the species level is important for choosing the proper antifungal treatment.