Marked potentiation of activity of beta-lactams against methicillin-resistant Staphylococcus aureus by corilagin

We found that an extract of Aretostaphylos uva-ursi markedly reduced the MI Cs of beta -lactam antibiotics, such as oxacillin and cefmetazole, against methicillin-resistant Staphylococcus aureus. We isolated the effective comp ound and identified it as corilagin. Corilagin reduced the MICs of various beta -lactams by 100- to 2,000-fold but not the MICs of other antimicrobial agents tested. The effect of corilagin and oxacillin was synergistic. Cori lagin showed a bactericidal action when added to the growth medium in combi nation with oxacillin.