Role of lipids in augmenting the antibacterial activity of benzoyl peroxide against Propionibacterium acnes.

Antimicrobial activity and physicochemical properties of benzoyl peroxide (BP) were investigated to determine the mechanism of action for the compound as an antiacne agent. The MICs and MBCs against nine strains of Propionibacterium acnes ranged between 100 and 800 micrograms/ml in a nutrient broth system, with a median fourfold increase in activity demonstrated when lipid was added. The partition coefficient of BP in a 50:50 artificial skin lipid and water system was greater than 2,500, with the concentration of BP soluble in lipid measured at 1.12% and in water at 0.005%. When BP was incubated in the presence of a lipid mixture, reaction products were formed, with evidence that at least some of these compounds possessed antibacterial activity. These results suggest that BP reduces the P. acnes numbers in sebaceous follicles because of good lipid solubility and interaction with the lipid component, the latter property contributing to the antimicrobial activity of the compound in a high-lipid environment.