Comparison of the in-vitro activities of the topical antimicrobials azelaic acid, nitrofurazone, silver sulphadiazine and mupirocin against methicillin-resistant Staphylococcus aureus
The in-vitro activities of the topical agents azelaic acid, nitrofurazone, silver sulphadiazine and mupirocin have been determined against 80 strains of MRS A collected from worldwide sources. MICs were determined by agar dilution (with an inoculum of approximately 5·0×l05cfu) in Iso-Sensitest agar, and MBCs were measured by replica-plating from MIC plates using velvet pads. The agents tested were uniformly active against MRSA, mupirocin being the most active (MIC50 0·15 mg/L) followed by nitrofurazone (MIC50 19 mg/L), silver sulphadiazine (MIC50 85 mg/L) and azelaic acid (MIC50 850 mg/L). Concentrations of azelaic acid, nitrofurazone and silver sulphadiazine close to the MIC were bactericidal, but mupirocin was only bactericidal at concentrations substantially greater than the MIC. In time-kill experiments, azelaic acid and nitrofurazone were gradually bactericidal, silver sulphadiazine was rapidly bactericidal and mupirocin was not bactericidal. Silver sulphadiazine killed sulphonamide-sensitive and sulphonamide-resistant strains equally rapidly. No resistant mutants were found to azelaic acid, nitrofurazone or silver sulphadiazine in an inoculum of 109 cfu, but two strains yielded (frequency: 1·0×10−9) mutants resistant to mupirocin. Our in-vitro results suggest azelaic acid, nitrofurazone and silver sulphadiazine could be of use for clearing staphylococcal carriage.