Effect of pre-exposure to protective bacterial cultures in food on Listeria monocytogenes virulence

Abstract

Protective cultures (PCs) are capable of inhibiting the growth of foodborne pathogens, including Listeria monocytogenes, in food products. However, their ability to attenuate pathogen virulence in food remains uninvestigated. In this study, we used an immunomagnetic separation approach to isolate the effect of pre-exposure to commercially produced PCs in milk as a model food on the subsequent ability of L. monocytogenes to survive simulated gastrointestinal conditions and infect human Caco-2 epithelial cells. Pre-exposure to two cultures of Lactiplantibacillus plantarum reduced the ability of L. monocytogenes to survive simulated gastrointestinal conditions with counts 2.7 log CFU/mL lower than control. The ability of L. monocytogenes to invade Caco-2 cells was also reduced by 1.5 and 2.3 log CFU/mL compared to control after exposure to Lactococcus lactis subsp. lactis and a strain of Lactiplantibacillus plantarum, respectively. All Lactococcus lactis and Lactiplantibacillus plantarum cultures were able to limit the pathogen translocation across Caco-2 cells by 1.5–2.1 log CFU/mL less than that of control. When coupled with their antimicrobial activities against L. monocytogenes, these results demonstrate the ability of PCs to enhance the safety of food products by also attenuating the pathogen virulence, thereby impeding its ability to cause infection upon ingestion.