Escherichia coli O157:H7 produces Shiga toxin (Stx) which is heat stable and causes Hemolytic Uremic
Syndrome (HUS), a serious disease associated with bloody diarrhea and even death. To ensure food
safety, both live E. coli O157:H7 and its toxin production in food products need to be controlled. Natural
ingredients with inhibitory effects on E. coli O157:H7 growth and toxin production are top choices of
antimicrobials for the food industry. The objectives of this study were to evaluate efficacy of grape seed
extract (GSE) against the growth, swimming motility and Stx production of E. coli O157:H7. The disc
diffusion assay indicated that 3.2 mg GSE per disc resulted in an inhibition zone of 14.8 ± 0.21 mm. The
minimal inhibitory concentration of GSE against E. coli O157: H7 was 4.0 mg/ml. At high inoculation level
(1 107 CFU/ml), including GSE at 0.25e2.0 mg/ml reduced Stx production without inhibiting E. coli
O157:H7 growth. At 5 105 CFU/ml inoculation level, 2.0 and 4.0 mg/ml GSE effectively inhibited the
growth of E. coli O157:H7 for at least 72 h, however, a low level of GSE (0.125e1.0 mg/ml) enhanced E. coli
O157:H7 growth and Stx2 production. At 4 mg/ml, GSE completely abolished Stx2 production in addition
to it bactericidal effect against E. coli O157:H7. In addition, GSE at concentration as low as 0.125% blocked
the swimming motility, which is important for E. coli O157:H7 surface adherence. In conclusion, GSE is
effective in inhibiting the motility of E. coli O157:H7, GSE shows potential to be used as a natural antimicrobial
to control E. coli O157:H7.