Assessment of Escherichia coli O157:H7-specific bacteriophages e11/2 and e4/1c in model broth and hide environments

Abstract

The efficacy of bacteriophages e11/2 and e4/1c as potential biocontrol agents for Escherichia coli O157:H7 in food applications was assessed under conditions relevant to the food chain environment. The stability of each phage was determined following exposure to varying environmental conditions (pH, temperature, water activity, and sodium chloride) and the ability of each phage to infect and reduce E. coli O157:H7 numbers under selected conditions was also examined. Both e11/2 and e4/1c significantly (p<0.05) reduced numbers of E. coli O157:H7 when exposed to pH values ranging from pH>4 to pH 9, temperatures from 4 °C to 37 °C, water activity values of 0.87 or 0.91 to 1.00 and NaCl concentrations of 1% to 2.5%. Subsequently, a cocktail of both phages was used (e11/2 and e4/1c) to assess reduction of E. coli O157:H7 on cattle hide pieces. This involved inoculating pieces of hide (20×20 cm) with E. coli O157:H7 (approximately 10⁶cfu/cm²) which were subsequently treated with either a suspension of a phage cocktail, consisting of e11/2 and e4/1c (multiplicity of infection of 1000 and 10,000, respectively) or water or not treated. Two different investigations were carried out; immediately or 1h after treatment application was performed in different experiments. Swab samples taken immediately after phage treatment showed no significant (p>0.05) reduction of E. coli O157:H7 numbers compared to the water treated or untreated samples. However, an extended exposure time of 1h following phage application revealed a significant reduction (p<0.05) (1.5 log₁₀ cfu/cm² reduction) in E. coli O157:H7 numbers compared to the numbers recovered on samples treated with water only. These findings demonstrate the potential use of e11/2 and e4/1c phages as a biocontrol agent for E. coli O157:H7 within various stages of the food chain, including on cattle hide.