Isolation and Characterization of Bacteriophages Targeting Non-O157 Shiga-toxigenic Escherichia coli

Introduction: Bacteriophages have been extensively beneficial in human and veterinary medicine, however, their application in foods is still limited. The recent FDA-approval of Listeria monocytogenes-specific-phage in meat and poultry has encouraged research into other phage-based products for food industry. One such application is their use as biocontrol agents against Shiga-toxigenic Escherichia coli (STEC). However, their application in foods requires them to be stable in a food matrix, especially in ready-to-eat and cooked products.

Purpose: Isolation and characterization of bacteriophages specifically targeting non-O157 Shiga-toxigenic Escherichia coli.

Methods: Bacteriophages, isolated from cattle operations in Oklahoma, were tested for lytic activity against 6 non-O157 STEC serogroups (O121, O145, O111, O103, O26, O45) using spot-on-lawn assay. Bacteriophages were purified and their morphology determined using transmission electron microscope (TEM). Thermal resistance was determined between 40-90°C for 60 minutes with 10-minute-sampling-intervals. Stability at various pH ranges (1-11) was analyzed at 37°C with sampling times between 1-24 h.

Results: Several bacteriophages (n=44) were isolated that exhibited inhibition towards non-O157 STEC. Except for the O45-specific phage, all other phages showed multiple-target-specificity. For example, O26-specific phage also showed lytic activity against O103 and O145 STECs. The TEM micrographs placed the O45, O26, O103, O145, and O121 phages into Myoviridae family except one O45-phage in Tectiviridae and one each of O103 and O26-phage in Siphoviridae family. The O111-phages belonged to the Siphoviridae family. Bacteriophages were very stable at 40-60°C; some (O111, O103, O45) lost activity at 70°C after 30 minutes; and all lost activity at 90°C after 10 minutes, except O121 and O26 phages. Phages had high infective ability between pH range 5.0-11.0 with the exception of O26-phage, showing infective ability at pH 1.0 and 2.0 for 2 h.

Significance: Bacteriophages showing high lytic activity towards non-O157 STECs, that are also pH and thermal stable, could serve as bio-preservatives in the food industry.