Internalization of Escherichia coli O157:H7 in fresh-cut vegetables under different conditions and the role of surface appendages in internalization.

Abstract

E. coli O157:H7 colonizes the surface of vegetables and subsequently penetrates the interior, posing a risk of foodborne illness. Our study investigated the internalization ability of E. coli O157:H7 in lettuce, spinach, red cabbage, and cucumber at different inoculum levels and temperatures, as well as the effect of slightly acidic electrolyzed water (SAEW) on E. coli O157:H7 internalization. Results showed that the higher the inoculation level and temperature, the higher the internalized population. SAEW promoted the internalization of E. coli within a certain range of available chlorine concentration. Furthermore, E. coli O157:H7 internalized vegetables mainly through stomata and wounds. We explored the process and location of E. coli O157:H7 internalization in cucumbers. Its internalization ability in cucumber fruit tissues was as follows: vascular bundles tissue > mesophyll > placental tissue > seed / center. The roles of flagella-related genes (fliS, fliD, and motA), pili-related genes (fimA and ppdD), and curli gene (csgB) in internalization were different. Genes fliS, fliD, motA, fimA, and ppdD affected internalization while csgB had no significant effect. The effects of these genes on the motility of E. coli O157:H7 were different. These findings provide insights into the role of flagella, pili and curli in bacterial internalization, aiding in the control of internalized bacteria by motility.