This study evaluated the internalization and cooking susceptibility of seven individual Escherichia coli (STEC) serogroups in surface-inoculated (105 log CFU/cm2) 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.