A.R. Parks

Internalization and thermal susceptibility of Shiga toxin-producing Escherichia coli (STEC) in marinated beef products

This study evaluated the internalization and cooking susceptibility of seven individual Escherichia coli (STEC) serogroups in surface-inoculated (10(5)log CFU/cm(2)) and vacuum tumbled marinated (30 or 60 min) bottom sirloin steaks. After storage for 14 days (0 to 2°C), flaps were cooked to various endpoint temperatures (55, 60, 65, and 71°C) for evaluation of pathogen survival by direct plating or rapid PCR based detection (BAX®). Direct plating of cooked samples yielded no enumerable plates. The data indicate varied internalization, translocation, and heat susceptibility patterns among serogroups. Using the rapid PCR based detection method O26, O103, and O111 were detected in flaps after cooking to 55 and 60°C, while O157:H7 survived in flaps cooked to 60 and 65°C. However, STEC O145 was the only serogroup that survived in all cooking temperatures. Serogroup O121 was not detected by plating or PCR in any cooked products. Intriguingly, STEC serogroups can be internalized during marination and the internalized pathogens vary in thermal susceptibility.

The influence of beef quality characteristics on the internalization and thermal susceptibility of Shiga toxin-producing Escherichia coli (STEC) in blade-tenderized beef steaks.

The risk of Shiga toxin-producing Escherichia coli (STEC) survival in blade-tenderized beef is a concern for beef processors. This study evaluated the internalization and post-cooking survival of individual STEC serogroups (O157:H7, O26, O45, O103, O111, O121, and O145) in blade-tenderized beef steaks with different quality traits. Strip loins representing four combinations of USDA Quality Grade (Choice or Select) and pH category (High pH or Normal pH) were inoculated (10(6)logCFU/cm(2) attachment) with individual STEC serogroups before storage (14 days), blade tenderization, and cooking (50, 60, 71, or 85°C). Serogroup populations on raw steak surfaces and internal cores were determined. Rapid-based methods were used to detect the internal presence of STEC in cooked steaks. Internalization and post-cooking survival varied among STECs. All serogroups, except O45 and O121, were detected in the internal cores of steaks cooked to 50°C, while O103, O111, and O145 STEC were detected in steaks cooked to 50, 60, and 71°C.