Effects of simulated food processing stresses on antibiotic resistance in Salmonella Typhimurium

Antibiotic resistance in Salmonella enterica poses a growing food safety concern. Sublethal environmental stresses during food processing, storage, and transportation may influence bacterial resistance phenotypes. This study investigated the effects of simulated food processing stresses including heat, refrigeration, freezing, acid, and alkaline conditions on the survival and antibiotic resistance of S. Typhimurium. The mechanisms underlying antibiotic resistance changes were further explored using scanning electron microscopy (SEM), extracellular ATP content quantification, and analysis of resistance-related and stress response gene expression. The results demonstrated that the antibiotic resistance in S. Typhimurium was influenced by both the type and duration of stress exposure. Resistance to aminoglycoside and β-lactam antibiotics increased following heat and cold stresses, whereas fluoroquinolone and β-lactam resistance was more prominent under acidic and alkaline conditions. Prolonged exposure to thermal or cold stress led to a time-dependent enhancement of resistance levels. SEM observations and elevated extracellular ATP levels after heat treatment revealed significant outer membrane disruption and cellular content leakage, suggesting increased membrane permeability. These membrane changes, along with transcriptional alterations such as the upregulation of resistance genes (e.g., bla_TEM) and stress response regulators (dnaK), as well as the downregulation of porin-encoding genes (ompF), likely contributed to the observed resistance changes. Overall, the findings underscore the potential of food chain-associated environmental stresses to induce adaptive responses and promote antibiotic resistance in S. Typhimurium. This highlights the importance of considering such effects during food processing, transportation, and storage, to support improved microbial risk management and safeguard public health.