Marked Potentiation of Activity of β-Lactams against Methicillin-Resistant Staphylococcus aureus by Corilagin

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