Theasinensin A, a Tea Polyphenol Formed from (-)-Epigallocatechin Gallate, Suppresses Antibiotic Resistance of Methicillin-Resistant Staphylococcus aureus

When (-)-epigallocatechin gallate (EGCG), the main constituent of tea polyphenols, was kept in a neutral buffer, it decomposed rapidly to give theasinensin A as the major product. Theasinensin A suppressed the oxacillin resistance of methidllin-resistant Stphylcoccus aureus (MRSA). In the presence of theasinensin A (3.5 × 10^-5 M), the minimum inhibitory concentrations (MICs) of oxacillin decreased from 256 or 64 μg/mL to 4 μg/mL for the MRSA strains used. The presence of this compound (3.5 × M^-5) also decreased the MIC of other β-lactam (penicillin G, from 32 μg/ mL to 0.125-0.5 μg/mL; ampicillin, from 16-32 μg/ml to 0.5-1 μg/mL) and aminoglycoside (streptomycin, from 4- 16 μg/mL to 0.125 -4 μg/mL) antibiotics for the MRSA strains.