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 × 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 × 10 - 5 M) 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. Abbreviations CFU:colony forming unit CSMHB:cation-supplemented Mueller-Hinton broth DETAPAC:diethylenetriaminepentaacetic acid EGCG:(-)-epigallocatechin gallate HPLC:high-performance liquid chromatography MIC:minimum inhibitory concentration MRSA:methicillin-resistant Staphylococcus aureus MSSA:methicillin-sensitive Staphylococcus aureus NMR:nuclear magnetic resonance PBP2′:penicillin-binding protein 2′
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Hatano et al. (2003) studied this question.