Different susceptibilities of Staphylococcus and Gram-negative rods to epigallocatechin gallate

We examined the antibacterial effects of epigallocatechin gallate (EGCg, the main constituent of tea catechins) against various strains of Staphylococcus and Gram-negative rods. Compared to the minimum inhibitory concentrations (MICs) of EGCg against S. aureus, S. epidermidis, S. hominis, and S. haemolyticus (50–100 µg/ml), higher MICs (≧800 µg/ml) were observed against Gram-negative rods, including Escherichia coli, Klebsiella pneumoniae, Salmonella typhi, Proteus mirabilis, Pseudomonas aeruginosa, and Serratia marcescens. And difference was observed between the binding abilities of EGCg with viable S. aureus and with E. coli. The bactericidal activity of EGCg for S. aureus was blocked dose-dependently by purified peptidoglycan but not by lipopolysaccharide or dextran. It was also found that peptone and protein, but not amino acids, in the culture medium greatly affected the antibacterial activity of EGCg. These results indicate that the structure of the bacterial cell wall and the different affinities of EGCg with the various cell wall components are responsible for the different susceptibilities of Staphylococcus and Gram-negative rods to EGCg.