Reactive oxygen species and the bacteriostatic and bactericidal effects of isoconazole nitrate

Bacterial superinfections often occur in dermatomycoses, resulting in greatly inflamed or eczematous skin. The objective of this study was to evaluate the antibacterial efficacy of isoconazole nitrate (ISN), a broad-spectrum antimicrobial imidazole, commonly used to treat dermatomycoses. Several gram-positive bacteria minimal inhibitory concentrations (MICs) for ISN (ISN solution or ISN-containing creams: Travogen or corticosteroid-containing Travocort) and ampicillin were obtained using the broth-dilution method. Speed of onset of the bactericidal effect was determined with bacterial killing curves. Reactive oxygen species (ROS) were visualised by staining cells with singlet oxygen detector stain. Compared with ampicillin MICs, ISN MICs for Bacillus cereus, Staphylococcus haemolyticus and Staphylococcus hominis were lower and ISN MICs for Corynebacterium tuberculostearicum and Streptococcus salivarius were similar. Incubation with ISN led to a 50% kill rate for Staphylococcus aureus and methicillin-resistant strains (MRSA). Post-ISN incubation, 36% (30 min) and 90% (60 min) of S. aureus cells were positive for ROS. Isoconazole nitrate has a broad bacteriostatic and bactericidal action, also against a MRSA strain that was not reduced by the corticosteroid in the Travocort cream. Data suggest that the antibacterial effect of ISN may be ROS dependent. An antifungal agent with robust antibacterial activity can provide a therapeutic advantage in treating dermatomycoses with suspected bacterial superinfections.