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Interactions of human pathogens with plants in the postharvest environment

Maria Brandl: Produce Safety and Microbiology Research Unit, USDA/ARS

<div>Foodborne pathogens such as <em>Salmonella enterica</em> and Shiga toxin-producing <em>E. coli</em> have the ability to achieve high densities in compromised plant tissue, which is otherwise not as hospitable to human pathogens as the intestinal milieu. The high number of foodborne illness outbreaks linked to minimally processed vegetables indeed point to a role of plant lesions in this emergence. Transcriptomic studies showed that enteric pathogens draw from complex nutrient pools in wounded or diseased leaf tissue. Additionally, transcriptomics revealed a considerable overlap in <em>S. enterica</em> physiology in soft rot lesions and in the chicken intestine, suggesting that the plant habitat is not as foreign to human pathogens as previously hypothesized. However, enteric pathogens also must contend with physicochemical stresses in damaged tissue resulting from plant cell leakage and defense response to injury and infection. Antimicrobial, osmotic, and oxidative stress response regulons were induced in <em>E. coli</em> O157:H7 in cut lettuce. <em>Ec</em>O157:H7 gained osmoprotection in lettuce wounds from plant-derived choline and its conversion to glycine betaine. Furthermore, upregulation of the SoxR regulon in <em>Ec</em>O157:H7 in cut lettuce enhanced its survival to sanitizer used in the food industry. Current knowledge suggests that damaged plant tissue does not merely supply enteric pathogens with substrates for growth but also mediates their protection at the site of injury or further in the postharvest environment.</div>