Effect of Food Components on Growth of Escherichia coli O157

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Escherichia coli O157 was first recognized as a cause of illness in 1982. Bovine products have most often been implicated in food-borne infections with E.coli O157. However recent outbreaks indicate that other food types may also serve as vehicles of transmission for this pathogen. E.coli O157 strains are reported to be tolerant to low pH and low water activity. In particular, the acid tolerance is important property of E.coli O157 because E.coli O157 must pass through the acidic gastric barrier to cause gastrointestinal disease. Acid resistance of E.coli O157 cells depends on their growth conditions. To clarify the reason for the infection of this pathogen, the survival and growth of E.coli O157 in foods were investigated. The productin of verotoxin by E.coli O157 in foods was also investigated.When E.coli O157 : H7 was incubated with the various seasonings, the O157 strains showed a high tolerance to soy sauce. E.coli O157 strains incubated with 12.5% soy sauce grew well, but the viable non-pathogenic E.coli populations were reduced. When the O157 strains were inoculated on LB agar media containing 14% soy sauce, all three E.coli O157 : H7 strains formed visible colonies, but all three non-pathogenic E.coli strains could not form visible colonies.When the E.coli cells were incubated with ethanol-soluble fractions of various spices, the E.coli O157 strains showed lower survival ratios in an ethanol-soluble fraction of nutmeg. The population of non-pathogenic E.coli was not reduced under the same conditions. The nutmeg extract may be useful for specific sterilization of E.coli O157.The acid resistance of E.coli O157 grown in vegetables was found to be low in comparison with that of the cells grown in EC medium.The production of verotoxin in E.coli O157 grown in EC medium was clearly higher than that of verotoxin in E.coli O157 grown in vegetable extracts. This suggest that some components of vegetables might prevent E.coli O157 from producing verotoxin.