Adhesion mechanism and biofilm formation of Escherichia coli O157:H7 in infected cucumber (Cucumis sativus L.).

Cucumber is usually eaten as a raw vegetable and easily contaminated by pathogenic microorganisms; the contamination process includes colonization, proliferation, and biofilm formation. In this study, plate counting was used to determine the stage of E. coli O157:H7 colonization/proliferation in cucumber epidermis and fruit. Expression of E. coli genes associated with adhesion, movement and oxidative stress response during colonization and proliferation in cucumber was evaluated with fluorescence real-time quantitative PCR. Scanning electron microscopy imaging was used to observe biofilm formation over time in different cucumber tissues at 4 °C and 25 °C. During colonization (at 0-45 and 0-30 min in epidermis and fruit, respectively), escV, fliC, espA, escN, espF, espG, espZ, nleA, tir, and ycbR genes were upregulated. The escC was downregulated, while map and espH expression did not vary. During proliferation (after 45 and 30 min in epidermis and fruit, respectively), fliC was downregulated, whereas the outer membrane protein intimin gene and oxidative stress genes rpoS and sodB were upregulated. During storage, 25 °C was more favorable for biofilm formation than 4 °C. The ability of biofilm formation on the vascular system was the strongest, and the biofilm on epidermis sloughed off earlier than that on other tissues. Clarifying the process of E. coli O157:H7 contaminating cucumbers provided useful information for the development of prevention and control methods of fresh-cut cucumber.