Survival of Escherichia coliO157:H7 and Salmonella spp. in Acidic Condiments

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Abstract
This study examined the effects of adaptation to acid and storage temperature on the survival of a nonpathogenic Escherichia coli strain, three strains of E. coli O157:H7, and three strains of Salmonella spp. in ketchup, mustard, and sweet pickle relish. Stationary-phase cells were adapted to acidic conditions in pH 5.0 Trypticase soy broth for 4 h at 37°C. Samples inoculated with individual strains (105 CFU/g for E. coli and 106 CFU/g for Salmonella spp.) were stored at 5 and 23°C. Numbers of surviving cells were determined by plating on Trypticase soy agar. Acid adaptation enhanced the survival of all three Salmonella strains (ATCC 6962, 13311, and 25957) and all three E. coli O157:H7 strains (ATCC 43889, 43894, and 43895), with the magnitude of the effect depending on the strain and storage temperature. Acid adaptation enhanced survival of the nonpathogenic E. coli strain at 5°C, but not at 23°C. Cells of all tested strains survived longer at 5°C than at 23°C. In general, the E. coli O157:H7 strains su...

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