Survival of Escherichia coli O157:H7 in cucumber fermentation brines

Authors: Breidt, Frederick; Caldwell, Jane

Submitted to: Journal of Food Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/25/2001
Publication Date: 4/1/2011
Citation: Breidt, F., Caldwell, J.M. 2011. Survival of Escherichia coli O157:H7 in cucumber fermentation brines. Journal of Food Science. 76(3):M198-M203.

Interpretive Summary: The safety of acid and acidified foods is threatened by acid resistant disease causing bacteria, including pathogenic E. coli strains. Acid resistant E. coli strains have caused disease outbreaks, and in some cases death, in a variety of foods, including spinach, sprouts, ground beef, and apple cider. It is known that this organism can survive for extended periods in fermented apple cider. Although no outbreaks have occurred in fermented vegetable products, these foods (which have similar pH values to apple cider) may also be at risk. We examined the survival of pathogenic E. coli strains in fermenting vegetables to determine the survival times and the conditions needed to ensure safety. Temperature, pH, and acid concentration were critical factors in assuring safety. In this study, pH was found to be the most important factor influencing cell survival, and the relationship between fermentation pH and cell death was measured. Producers of fermented vegetables can use these data to help assure safety of their products.

Technical Abstract: Bacterial pathogens have been reported on fresh cucumbers and other vegetables used for commercial fermentation. The Food and Drug Administration currently has a 5-log reduction standard for E. coli O157:H7 and other vegetative pathogens in acidified pickle products. For fermented vegetables, which are acid foods, there is little data documenting the conditions needed to kill acid resistant pathogens. To address this knowledge gap, we obtained 10 different cucumber fermentation brines at different stages of fermentation from 5 domestic commercial plants. Cucumber brines were used to represent vegetable fermentations because cabbage and other vegetables may have inhibitory compounds that may affect survival. The 5-log reduction times for E. coli O157:H7 strains in the commercial brines were found to be positively correlated with brine pH, and ranged from 3 to 24 d for pH values of 3.2 to 4.6, respectively. In a laboratory cucumber juice medium that had been previously fermented with Lactobacillus plantarum or Leuconostoc mesenteroides (pH 3.9), a 5-log reduction was achieved within 1 to 16 d depending on pH, acid concentration, and temperature. During competitive growth at 30 °C in the presence of L. plantarum or L. mesenteroides in cucumber juice, E. coli O157:H7 cell numbers were reduced to below the level of detection within 2 to 3 d. These data may be used to aid manufacturers of fermented vegetable products determine safe production practices based on fermentation pH and temperature.