Antifungal susceptibility profiles of Onychomycosis caused by different species of Fusarium

Background: Onychomycosis is a common fungal infection of the nails that accounts for approximately 50 % of all onychopathies. Among NDMs, Fusarium spp. is the most frequently isolated fungus in nail infections in Brazil. Our goal was to describe the profile of in vitro activity to antifungal in 35 isolates of Fusarium spp.

Methods: The susceptibility testing to five antifungals were performed according to Clinical and Laboratory Standards Institute methods (CLSI M38-A2) against isolates of Fusarium spp from nails of hand and foot of patients, attending a tertiary-care hospital in Brazil during the period July to September 2015. Identification of species was based on DNA sequences of ribosomal internal transcribed spacer as previously described.

Results: In general, Fusarium spp. show in vitro resistance to the available the antifungal agents. Amphotericin B was the most effective antifungal agent against the majority of the isolates with 60% of presenting MIC ≤4 µg/ml, followed by voriconazole with 34.2 % presenting MIC ≤4 µg/ml. Results of antifungal susceptibility testing in vitro indicate broad resistance to fluconazole, itraconazole and terbinafine, with MIC values >64 µg/ml (table 1).

Table 1. Minimum Inhibitory Concentrations (MICs) of antifungals agents for Fusarium solani species complex (FSSC) and Fusarium oxysporum complex (FOSC)
	MIC (µg/ml)
Species (n° of isolates)	Amphotericin B		Voriconazole		Itraconazole		Fluconazole		Terbinafine
	Range		Range		Range		Range		Range
Fusarium keratoplasticum (17)	1->16		0.5->32		>64		32->128		>64
Fusarium solani (3)	0.125-16		0.5->32		1->64		32->128		>64
Fusarium petroliphilum (2)	1-8		8-16		1->64		>128		>64
Fusarium falciforme (2)	4-8		0.5-16		>64		>128		>64
Neocosmospora rubicola (1)	4		8				128		>64
Fusarium oxysporum(10)	0.5-16		0.125-32		0.5->64		64->128		16->64
Total (35)	0.125-16		0.125-> 32		0.5->64		32->128		16->64

Conclusion: Fusarium species are highly prevalent in patients with onychomycosis. Amphotericin B has shown excellent in vitro activity against different Fusarium species. Except for voriconazole, Fusarium species have shown broad resistance to azoles including fluconazole and itraconazole. Terbinafine commonly used for treatment of onychomycosis has shown high MIC for all Fusarium species.