Effect of gastric pH and bile acids on the survival of Listeria monocytogenes and Salmonella Typhimurium during simulated gastrointestinal digestion

The human gastrointestinal tract (GIT) harbors numerous defensive mechanisms to impede pathogen colonization, including gastric acidity and bile acids in the small intestine. This study aims to elucidate the survival of Salmonella Typhimurium and Listeria monocytogenes under different levels of gastric pH (2.0–3.5) and bile acid concentrations (2.5 mM – 10.0 mM), during an in vitro digestion process following the ingestion of a contaminated food model system. The results showed that S. Typhimurium  was more susceptible to gastric acidity than L. monocytogenes, yet more bile acid tolerant. Interestingly, the bile acids bactericidal effect towards L. monocytogenes was higher if the previous exposure to the gastric acidity was harsher. Our findings suggest that, despite the different microbial behavior of the two species in the simulated GIT, the effects of gastric acidity and bile acids alone could not prevent their survival in the intestine. Industrial relevance S. Τyphimurium and L. monocytogenes represent biological threats that are of major concern for the food industry due to their ubiquitous nature and their ability to trigger foodborne illnesses. Their ability to survive the gastrointestinal passage is crucial for their subsequent intestinal colonization that can lead to host infection. Therefore, obtaining a deeper insight into the factors affecting pathogen survival in the gut is vital for the establishment of more efficient strategies to prevent foodborne diseases. Given the limitations and ethical constraints of conducting studies like this in vivo, the applied in vitro digestion model system along with the mathematical modelling can provide a valuable alternative that can be readily utilized in the food and pharmaceutical industry as a platform for similar digestion studies.