Influence of vitamin exposure on Escherichia coli O157:H7 attachment, stress response and virulence

Fresh produce is a natural source of vitamins in our diet. Additionally, our enteric flora produces several vitamins, including biotin, cobalamin, folate, menaquinone, pantothenate, and riboflavin. The aim of this study was to determine whether enterically-produced or food-related vitamins may increase attachment of Escherichia coli O157:H7 to leafy green produce, and trigger expression of key stress and virulence genes, thereby enabling its gastrointestinal survival. Late logarithmic phase E. coli O157:H7 grown in M9 minimal medium was exposed to α-tocopherol, ascorbate, biotin, cobalamin, folate, menaquinone, pantothenate, or riboflavin. Following 1.5 and 3 h exposure, HeLa cell assays were performed to assess adherence, while the impact of ascorbic acid, cobalamin and pantothenate on Shiga toxin (Stx) production was quantified by Stx ELISA. Expression of stress response genes (dnaK, osmC, rpoS) was monitored using lux-promoter fusions. Expression of relevant stress response and virulence genes was examined by a quantitative real-time polymerase chain reaction. Lastly, to determine attachment behavior, treated E. coli O157:H7 cells were spotted onto spinach leaves. Treatments with α-tocopherol, biotin, cobalamin, and pantothenate significantly increased adherence to HeLa cells (p1-log10 increase in adherence. Cobalamin treatment resulted in significantly increased Stx1 and 2 levels (p<0.001), while ascorbate and pantothenate led to lower levels (p