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Protective Effects of Organic Acids on Survival of Escherichia coli O157:H7 in Acidic Environments

Permanent URL:
http://handle.nal.usda.gov/10113/15857
File:
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Abstract:
Outbreaks of disease due to acid-tolerant bacterial pathogens in apple cider and orange juice have raised questions about the safety of acidified foods. Using gluconic acid as a noninhibitory low-pH buffer, we investigated the killing of Escherichia coli O157:H7 strains in the presence or absence of selected organic acids (pH of 3.2), with ionic strength adjusted to 0.60 to 0.68. During a 6-h exposure period in buffered solution (pH 3.2), we found that a population of acid-adapted E. coli O157:H7 strains was reduced by 4 log cycles in the absence of added organic acids. Surprisingly, reduced lethality for E. coli O157:H7 was observed when low concentrations (5 mM) of fully protonated acetic, malic, or L-lactic acid were added. Only a 2- to 3-log reduction in cell counts was observed, instead of the 4-log reduction attributed to pH effects in the buffered solution. Higher concentrations of these acids at the same pH aided in the killing of the E. coli cells, resulting in a 6-log or greater reduction in cell numbers. No protective effect was observed when citric acid was added to the E. coli cells. D-Lactic acid had a greater protective effect than other acids at concentrations of 1 to 20 mM. Less than a 1-log decrease in cell numbers occurred during the 6-h exposure to pH 3.2. To our knowledge, this is the first report of the protective effect of organic acids on the survival of E. coli O15:H7 under low-pH conditions.
Author(s):
Bjornsdottir, K. , Breidt, F. , McFeeters, R. F.
Subject(s):
Escherichia coli O157:H7 , pathogen survival , acidity , acid tolerance , malic acid , acetic acid , lactic acid , citric acid , food pathogens , food microbiology , protective effect
Format:
p. 660-664.
Note:
Includes references
Source:
Applied and environmental microbiology 2006 Jan., v. 72, no. 1
Language:
English
Year:
2006
Collection:
Journal Articles, USDA Authors, Peer-Reviewed
Rights:
Works produced by employees of the U.S. Government as part of their official duties are not copyrighted within the U.S. The content of this document is not copyrighted.