Additive, indifferent and antagonistic effects in combinations of epigallocatechin gallate with 12 non-β-lactam antibiotics against methicillin-resistant Staphylococcus aureus

Additive, indifferent and antagonistic effects were observed in combinations of epigallo- catechin gallate (EGCg, a main constituent of tea catechins) with12 non-β-lactam antibiotics against methicillin-resistant Staphylococcus aureus (MRSA). The combinations of EGCg with the inhibitors of either protein or nucleic acid synthesis showed additive or indifferent effects. These antibiotics included tetracycline, minocycline, chloramphenicol, streptomycin, genta- micin, kanamycin, erythromycin, rifampicin and ofloxacin. In contrast, EGCg showed an antagon- istic tendency against glycopeptide antibiotics (vancomycin, teicoplanin and polymyxin B). The common property of these antibiotics is the peptide backbone structure, suggesting a direct binding of EGCg with the antibiotics. The above results indicate that tea catechins may affect the activities of antibiotics both positively and negatively.