Growth and Inhibition by Acids of Five Species of Pathogenic Bacteria Inoculated in Salad Vegetables

The growth of Yersinia, Listeria monocytogenes, Escherichia coli O157, and Staphylococcus aureus in salad vegetables stored at 5°C, 10°C, and 25°C, and the initial reduction of the bacterial populations by treatment of the vegetables with organic acids were examined. The multiplication of Yersinia enterocolitica was observed in cabbage and radishes held at 5°C for 4 days, at 10°C for 2 to 3 days, and at 25°C for 1 day. That of Yersinia pseudotuberculosis was observed in radishes at 5°C for 3 days, at 10°C for 3 days and at 25°C for 1 day. That of L. monocytogenes was observed in radishes at 10°C for 3 days, and in cabbage and carrots stored at 25°C for 1 day. That of E. coli O157 was observed in cucumbers held at 10°C for 3 days and in all five kinds of vegetables held at 25°C for 1 day. Reduction of L. monocytogenes, E. coli O157, and S. aureus by log 2 cycles or more was observed within 2 days after treatment with fumaric acid. Following treatment with acetic acid and lactic acid, the reduction of the initial population of these bacteria was about log 1 cycle.