Sublethal cooking temperatures and simulated digestion: survival responses of Listeria monocytogenes and the emerging contaminant Acinetobacter spp.

The persistence of bacterial pathogens in food products, even after cooking and gastrointestinal exposure, poses a significant public health risk. This study aimed to evaluate the survival and adaptability of Listeria monocytogenes and Acinetobacter spp. (A. baumannii and A. johnsonii) in bovine burgers subjected to different cooking temperatures and subsequent digestion using the INFOGEST in vitro simulated gastrointestinal tract model. Burgers were inoculated separately with L. monocytogenes and Acinetobacter spp. and cooked at three temperature conditions: rare-cooked (45 °C), medium-cooked (55-65 °C), and well-done (≥70 °C). After cooking, samples were exposed to simulated gastrointestinal conditions. Cooking at mild-heat (55-65 °C) and high temperatures (≥70 °C) did not completely eliminate all tested bacteria, indicating their resilience under these conditions. Acinetobacter spp. exhibited significant adaptability to thermal processing, displaying notable tolerance to thermal and gastrointestinal stresses to both heat stress and gastrointestinal conditions. Among L. monocytogenes strains, strain 3524 demonstrated the highest resistance, surviving temperatures above 70 °C and subsequent exposure to acidic and bile-rich environments. In contrast to strain 3524, strain 2682 showed a protective effect from low-heat cooking; survival rates after gastrointestinal passage were actually higher in rare burgers (45 °C) than in raw burgers, suggesting a heat-induced stress adaptation. The results highlight the ability of Acinetobacter spp. to withstand sequential thermal and digestive stresses, suggesting its potential for adaptation in foodborne scenarios. The survival of the foodborne pathogen L. monocytogenes after cooking underscores the necessity for strict food safety measures. In particular, strain 3524 of L. monocytogenes proved high resistance to both high-heat cooking and gastrointestinal conditions, raising concerns about its persistence in the food chain. These findings emphasize the importance of proper cooking practices and additional food safety interventions to prevent bacterial survival and potential infection risks.