Osmotic stress tolerance and virulence of Salmonella enterica Tennessee and Serogroup B strains from low-moisture foods

Salmonella enterica is a major foodborne pathogen capable of surviving in low-water-activity (aW) foods and retaining the ability to invade intestinal epithelial cells after environmental stress, such as exposure to high salt concentrations. Although multiple serotypes tolerate low aW, Tennessee strains have been repeatedly linked to outbreaks in dry foods, suggesting specific adaptations. This study evaluated the effects of NaCl (1%, 4%, and 6%) on growth, biofilm formation, post-biofilm recovery, and internalization capacity (Caco-2 cell assays) of six S. enterica strains—four Tennessee and two serogroup B isolates—from peanuts, raisins, chocolate, and dehydrated tomatoes. Growth and biofilm formation were monitored over a 7-day exposure to NaCl; post-biofilm recovery and internalization were assessed afterward. While all strains showed reduced internalization after salt exposure, Tennessee isolates generally maintained higher growth and biofilm formation than the ATCC 14028 reference strain. Phenotypic responses varied by strain and NaCl concentration, indicating differences in osmotic stress adaptation. The persistence of internalization capacity, even at reduced levels, highlights a potential food safety risk in NaCl-preserved products. These findings emphasize the need to consider strain-specific traits when developing control measures for Salmonella in dry food environments.