Gamma Radiation Inactivation of Non-O157:H7 Shiga Toxin-producing Escherichia coli in Foods

Introduction: Non-O157:H7 serovars of shiga toxin-producing Escherichia coli are emerging foodborne pathogens that have been associated with illness outbreaks and food product recalls on a global basis. Ionizing (gamma) radiation is a nonthermal food safety intervention technology that has been approved for use in over fifty countries to improve the safety and shelf-life of foods.

Purpose: In this study, the use of gamma radiation to inactivate pathogenic E. coli in foods was investigated. 

Methods: A cocktail of six non-O157:H7 serovars, O26:H11, O45:H2, O103:H2, O111:H11, O121:H19, and O145, or six O157:H7 serovars was inoculated (10⁸ CFU/g) into ground beef (GB), ground turkey (GT), catfish fillets (CF), or shrimp (SH). Food samples (10 g) were placed in sterile poly-nylon sample bags, sealed under vacuum and then frozen for 3 min at -59°C using a Cryo-Test Chamber by exposing the samples to controlled liquid nitrogen vapor. The samples were then irradiated (0, 0.6, 1.2, 1.8, 2.4, and 3.0 kGy) using a self-contained 137-Cs gamma radiation source (0.074 kGy/min at -20°C). Duplicate samples were processed per experiment at each radiation dose, and each experiment was conducted 3 times.

Results: Radiation D-values (the radiation dose needed to inactivate 1 log of pathogen) for E. coli O157:H7 were 0.47, 0.46, 0.52, and 0.42 kGy in GB, GT, SH, and CF, respectively. The D-values for the non-O157:H7 serovars were 0.40, 0.34, 0.41, and 0.38 kGy in GB, GT, SH, and CF, respectively. With the exception of catfish, the D-values for the non-O157:H7 serovars were significantly lower (P < 0.05) than those for O157:H7.

Significance: These results indicate that the radiation doses used to inactivate E. coli O157:H7 in these foods can also be used for the non-O157:H7 serovars.