Cocktails of Plant-produced Colicins for Efficient Control of Major Pathogenic Strains of Escherichia coli

Introduction: Enteropathogenic Escherichia coli (EPEC), such as E. coli O157:H7, cause over 200,000 illnesses at a cost to the EU and U.S. economies of approximately €2 billion annually. Many of these illnesses have been linked to consumption animal products or, lately, organically grown vegetables.  Post-harvest intervention strategies with efficacy against the many different strains of EPEC are needed.  Colicins are antimicrobial proteins produced by and effective against certain E. coli strains. Several colicins have been shown to be highly effective against EPEC strains and in reducing EPEC populations in both live animals and on animal-derived products.  However, strain-to-strain variation in sensitivity to different colicins suggests that a mixture of several different colicins would be needed to be efficacious against a broad range of EPEC.

Purpose: To determine the efficacy of colicins with different modes of action against the “Big 7” EPEC strains.

Methods: Colicins M, E7, N, E1, and E3 were expressed in a highly efficient green-plant expression host.  This system provides high yields (up to 5 kg active protein per ton of fresh green biomass) and very low manufacturing costs.  Antimicrobial activity against pure cultures was determined in both soft-agar overlay assays and by enumeration from broth culture.

Results: Col M had the highest (P < 0.01) specific activity against O26, O45, O111, and O157.  Col M was not however efficacious against O121.  Of the colicins tested, only Col E7 and Col N had significant activity against O121.  Mixtures of Col M and Col E7, at a total quantity of 5 mg of colicin/kg of food product, caused significant (P < 0.01) reductions (2 - 6 logs) in EPEC from a variety of foods.

Significance: A cocktail of colicins would be a highly effective intervention strategy for the reduction of EPEC on a variety of food items.