Ikigai et al34 reported the results of their research on EGCg and
EC, two of the strongly antimicrobial catechins found in green tea.
They used E. coli K-12 strain G6 and Staphylococcus aureus
ATCC25932 as Gram-negative and Gram-positive bacteria, respectively.
EC and EGCg were extracted from water-soluble extract of
green tea. The minimal growth inhibitory concentration (MIC) was
determined by the agar dilution method. The MIC of EGCg for E. coli
and S. aureus were 573 mg/mL and 73 mg/mL respectively. The MIC of
EC for E. coli and S. aureus were >1145 mg/mL and 183 mg/mL,
respectively. Catechins had greater activity against Gram-positive
than Gram-negative bacteria. Liposomes were used as a model of
bacterial membranes. EC showed little absorption through liposome
membranes at 0.6 mM. They used EGCg to examine the effects
of catechin on bacterial membranes. EGCg inhibited cytoplasmic
membrane function by inducing leakage of small molecules from
the intraliposomal space. Therefore, catechins damaged bacterial
membranes and impaired membrane function.34