Inhibition of Staphylococcus aureus by Oleuropein Is Mediated by Hydrogen Peroxide

The inhibition of Staphylococcus aureus by oleuropein is shown to be largely due to hydrogen peroxide production by oleuropein. The reaction is initiated by noninhibitory levels of hydrogen peroxide present as a result of tryptone oxidation in the underlying medium. Inhibition is abolished by catalase and anaerobic incubation conditions, and the effect of tryptone can be replicated by exogenous H₂O₂. S. aureus strains with reduced catalase activity show greater sensitivity to oleuropein. A mechanism for hydrogen peroxide production is proposed. Inhibition is not entirely due to H₂O₂, since some organisms with similar sensitivity to H₂O₂ as S. aureus were resistant to oleuropein, suggesting that there may be a cooperative effect between H₂O₂ and oleuropein itself.