Purpose: The purpose of this study was to obtain bacteriophages specific for pathogenic Escherichia coli from environmental sources and evaluate their ability to control the host pathogen on fresh produce.
Methods: A phage active against E. coli O157:H7 EDL933, with a titer of 108 PFU/ml, was isolated from waste water. Cross-reactivity studies showed this phage had strong activity against eight of twelve additional E. coli strains. Application of phage for biocontrol was evaluated on green peppers. Cut peppers were treated with UV light to eliminate background biota, then spot-inoculated with E. coli O157:H7 EDL933 on cut edges. Inoculated pepper was dipped for 2 min in phage lysate, stored at room temperature, and plated periodically for up to 72 h. Control samples were dipped for 2 min in LB broth, the same medium used in the lysate, and analyzed at the same time intervals.
Results: Phage treatment inactivated 1 log E. coli/g pepper, compared to the initial load following rinsing, and 2 logs compared to the control population after 3 h. After 72 h this difference between the treatment and the control was reduced to 1 log due to recovery of surviving cells. Reductions could be increased by modifying experimental parameters such as dip time and titer.
Significance: These findings suggest the usability of bacteriophage to selectively control pathogens on fresh produce without damaging the product. Further testing is warranted to evaluate phage biocontrol in other food products as well.