Antibiotic Production by Dermatophyte Fungi

This study examined 32 clinical isolates of anthropophilic dermatophyte fungi for antibiotic production in liquid culture and on human stratum corneum. The researchers used agar diffusion bioassays and chromatographic analysis to detect and classify antibiotics. Twenty-four isolates produced antibiotics in liquid culture, with some strains producing multiple antibiotics. When grown on stratum corneum alone, only four isolates produced detectable antibiotics, but this number increased to eleven when an artificial sweat supplement was added as a nutrient source. All dermatophyte species tested produced benzyl penicillin-like substances. Notably, some Trichophyton isolates produced streptomycin-like antibiotics, a characteristic previously unreported in eukaryotic organisms. Epidermophyton floccosum produced additional uncharacterized antibiotics besides benzyl penicillin and azalomycin F. Antibiotic production occurred across normal skin temperature ranges, though the type and frequency of antibiotics detected were sometimes influenced by incubation temperature. These findings suggest that dermatophyte-produced antibiotics may influence the antibiotic resistance patterns of bacterial flora in infected skin lesions.

Key findings

• Twenty-four of thirty-two dermatophyte isolates produced antibiotics in liquid culture, with all species producing benzyl penicillin-like substances and some Trichophyton isolates producing streptomycin-like antibiotics, the latter being the first recorded production of streptomycin by eukaryotic organisms.
• Antibiotic production was more readily detected in synthetic fermentation medium than on natural stratum corneum, but supplementing skin strips with artificial sweat increased antibiotic detection from four to eleven isolates.
• Epidermophyton floccosum produced multiple antibiotic types including benzyl penicillin-like, azalomycin F-like, and uncharacterized antibacterial substances not found in other dermatophyte species.
• Antibiotic production occurred across physiologically relevant skin temperatures (26-33°C), with some variation in antibiotic type and detection frequency depending on incubation temperature.
• The natural antibiotic production by dermatophytes may contribute to antibiotic resistance in bacterial flora associated with fungal skin infections, potentially explaining variable resistance patterns observed in clinical lesions.