New insights on the antibacterial efficacy of miconazole in vitro

Summary Miconazole is a broad‐spectrum antifungal used in topical preparations. In the present investigation the minimal inhibitory concentration ( MIC ) of miconazole for eighty wild type strains of gram‐positive and gram‐negative bacteria isolated from infected skin lesions was assessed using a modified agar dilution test (adapted to CLSI , Clinical Laboratory Standards Institute). 14 ATCC reference strains served as controls. Miconazole was found efficacious against gram‐positive aerobic bacteria (n=62 species), the MIC s against Staphylococcus (S.) aureus , S . spp., Streptococcus spp. und Enterococcus spp. ranged between 0.78 and 6.25 μg/mL. Interestingly, there were no differences in susceptibility between methicillin‐susceptible ( MSSA , 3) methicillin‐resistant ( MRSA , 6) and fusidic acid‐resistant ( FRSA , 2) S. aureus isolate s . Strains of Streptococcus pyogenes (A‐streptococci) (8) were found to be slightly more sensitive (0.78‐1.563 μg/mL), while for gram‐negative bacteria, no efficacy was found within the concentrations tested ( MIC >200 μg/mL). In conclusion, for the gram‐positive aerobic bacteria the MIC s of miconazole were found within a range which is much lower than the concentration of miconazole used in topical preparations (2%). Thus topically applied miconazole might be a therapeutic option in skin infections especially caused by gram‐positive bacteria even by those strains which are resistant to antibiotics.