Effects of Grape Seed Extract on the Growth of Top Six Non-O157 Shiga Toxin-producing Escherichia coli

Introduction: Shiga toxin-producing Escherichia coli (STEC) is a leading cause of foodborne infections. Centers for Disease Control and Prevention (CDC) “top-six” non-O157 STEC are growing concerns to the food industry due to the rising foodborne illnesses from these strains. Given their ability to cause fetal hemolytic uremic syndrome and global prevalence in foods, developing intervention methods for these non-O157 strains is necessary, and natural ingredients are among top choices.  Grape seed extract (GSE) contains abundant polyphenols which have antimicrobial activity in addition to its health beneficial effects.

Purpose: The objective is to explore the inhibitory effects of GSE on the growth and swimming motility of the “top-six” non-O157 STEC.

Methods: Swimming motility was assayed using 0.3% LB agar plates. The growth curves were conducted in 96 well polystyrene microtiter plates.

Results: At 5×10⁵ CFU/ml inoculation level, 0.5-4 mg/ml GSE effectively inhibited the growth of O26:H11, while 4 mg/ml GSE prevented the growth of all other non-O157 STEC strains tested including O45:NM, O103:H2, O111:H2, O121:H19 and O145:NT.  However, GSE up to 4 mg/ml had a limited inhibitory effect on top-six non-O157 STECs when the initial inoculation level increased to 1×10⁷ CFU/ml.  In addition, GSE significantly inhibited swimming motility of O26:H11, O103:H2, O111:H2, O121:H19 and O145:NT at concentrations as low as 0.25 mg/ml, and completely blocked their motility at 4 mg/ml.

Significance: GSE can effectively inhibit swimming motility of non-O157 STEC, however, its inhibitory effects toward the growth are strain and population dependent. Such information is useful for its application as an antimicrobial in food industry.