Effect of salt addition on acid resistance response of Escherichia coli O157:H7 against acetic acid.

A combination of salt and acid is commonly used in the production of many foods, such as pickles and fermented foods. However, in our previous studies, addition of salt significantly reduced the inhibitory effect of acetic acid against E. coli O157:H7 in laboratory media and pickled cucumbers. Therefore, this study was conducted to determine the effect of salt addition on the acid resistance (AR) response of E. coli O157:H7 after treatment with acetic acid. The combined effect of acetic acid and salt showed different results depending on media tested. Organic compounds such as yeast extract and tryptone were required to observe the antagonistic effect of salt and acetic acid in combination. However, use of an rpoS mutant or addition of chloramphenicol resulted in no changes in the antagonistic effect of acetic acid and salt. The addition of glutamate to phosphate buffer significantly increased the survival levels of E. coli O157:H7 after the acetic acid treatment; however, the survival levels were lower than those after the treatment with acetic acid alone. Thus, the addition of salt may increase the AR response of E. coli O157:H7; however, these survival mechanisms were not proven clearly. Therefore, further studies need to be performed to better understand the antagonism of acetic acid salt against E. coli O157:H7.