Microplastic biofilms enhance environmental stress, disinfectant, and antibiotic tolerance of Salmonella enterica serovar typhimurium in simulated fresh vegetable processing systems.

Microplastics (MPs) are widely found in food supply chains. They act as a stable surface for microorganisms to stick to, which makes it more likely that pathogens will be present. This study aims to investigate the biofilm formation on MPs and evaluate the tolerance of foodborne pathogen Salmonella enterica serovar Typhimurium (ST) to environmental stresses, disinfectants, and antibiotics. The microplastics biofilms (MBs) were constructed on polyethylene MPs by the microbial samples from a vegetable washing sink. Microorganisms can form biofilms on MPs in the lettuce juice-based cultures. The biofilm structure and bacterial community exhibited a succession with the incubation periods. The presence of opportunistic pathogenic genera was identified. ST can successfully colonize preformed MBs, and its environmental stress tolerance to UV radiation, desiccation, and nutrient deprivation was significantly enhanced. Concurrently, mixed-species MBs enhanced the ST tolerance to BAC (Benzalkonium chloride), NaClO and PCMX (Chloroxylenol) disinfectants, and tolerance to ampicillin. These were linked to the upregulation of efflux pumps (acrAB, tolC) and tolerance regulators (phoPQ, oxyR). Genetic analysis revealed a significant upregulation of the ST virulence-associated genes (sipC, csrA, prgJ, sptP, barA, rstA). These findings emphasized the emerging threat of microplastic-biofilm synergistic contamination to food safety, and there is an urgent need to explore the transmission mechanisms and control strategies in the actual food supply chain.