The inhibitory effects of green tea polyphenol epigallocatechin gallate (EGCG) on virulence phenotypes and gene expression regulated by quorum sensing (QS) in Escherichia coli O157:H7 were demonstrated at concentrations of 1 to 100 μg/ml, which are lower than the MIC (539 ± 22 μg/ml). At 25 μg/ml, the growth rate was not affected, but autoinducer 2 concentration, biofilm formation, and swarm motility decreased to 13.2, 11.8, and 50%, respectively. Survival at 5 days of nematodes (Caenorhabditis elegans) that were fed the pathogen without and with EGCG were 47.1 and 76%, respectively. Real-time PCR data indicated decreased transcriptional level in many quorum sensing–regulated virulence genes at 25 μg/ml. Our results suggest that EGCG at concentrations below its MIC has significant antipathogenic effects against E. coli O157:H7.
† Present address: Molecular Hematology, Catholic University, Seoul 110-758, Korea.