Spatial growth of major foodborne pathogens in food-like matrices alters food-related stress responses and gastrointestinal tolerance

Foods are spatially heterogeneous matrices in which microbial pathogens often grow as immobilised microcolonies rather than as freely suspended planktonic cells. We investigated how spatial growth in food-like semi-solid matrices affects responses to food-related stresses and subsequent tolerance to gastrointestinal conditions in eight major foodborne pathogens. Planktonic and spatialised populations were compared under salt and organic acid stresses. Spatial growth modified bacterial growth dynamics in a species-, stress- and concentration-dependent manner. More importantly, prior growth in gelled food-like matrices enhanced tolerance to simulated gastrointestinal stresses in vitro, particularly under acidic conditions. In Salmonella enterica , this protective effect was also observed in vivo in the acidic midgut of Hermetia illucens larvae, with significantly higher recovery (~ 2 log CFU/larva) after prior growth under high salt conditions. These findings show that spatial organisation can markedly modulate pathogen stress tolerance and should be considered in predictive microbiology and food safety assessment.