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 methicillin-resistant Staphylococcus aureus (MRSA). In the presence of theasinensin A (3.5 x 10(-5) M), the minimum inhibitory concentrations (MICs) of oxacillin decreased from 256 or 64 microg/mL to 4 microg/mL for the MRSA strains used. The presence of this compound (3.5 x 10(-5) M) also decreased the MIC of other beta-lactam (penicillin G, from 32 microg/mL to 0.125-0.5 microg/mL; ampicillin, from 16-32 microg/mL to 0.5-1 microg/mL) and aminoglycoside (streptomycin, from 4 - 16 microg/mL to 0.125-4 microg/mL) antibiotics for the MRSA strains.