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United States Department of Agriculture

Agricultural Research Service

Research Project: INVESTIGATION OF ACID RESISTANCE OF ESCHERICHIA COLI STRAINS
2013 Annual Report


1a.Objectives (from AD-416):
The purpose of this study is to determine the survivability of Escherichia coli strains isolated from five sources (foods, bovine carcasses, bovine feces, water, and human) in acetic acid solutions under conditions that are typical of acidified foods.


1b.Approach (from AD-416):
The survivability of Escherichia coli strains in acidified foods will be investigated under a variety of environmental conditions. Pure and mixed culture cell suspensions will be tested to determine acid resistance under various atmospheric conditions, pH values, and ionic strengths. The genetic relationships between strains will be characterized to determine if there are correlations between genotype and acid resistance phenotype. Genes relating to acid resistance may be identified.


3.Progress Report:

This project is related to in-house project objective 3: To determine the survival of E. coli O157:H7 in commercial fermentation brines, with and without competing microflora, and under a variety of extrinsic and intrinsic conditions.

Research was done to investigate the acid resistance of 100 or more pathogenic Escherichia coli serotypes, including outbreak strains such as Escherichia coli O157:H7, and Escherichia coli O104:H4. The ability of these strains to survive in acid solutions at different pH values was determined using a standardized set of conditions that allowed direct comparison of strains from different sources and having different serotpyes. For selected groups of strains, genetic similarity was also determined. Data from acid resistance comparison experiments showed that isolates from animal and environmental sources (bovine carcass, bovine feces, waterborne) were significantly more acid resistant as a group than human isolates. Some serotypes as a group were also more acid than others, although no direct correlation with acid resistance and human disease was determined. The development of acid tolerance by foodborne pathogenic bacteria may be signifcant at several points along the farm-to-table continuum of food production. It is important to understand how previous environment and processing conditions can affect the acid tolerance status of foodborne Escherichia coli O157:H7 in order to devise strategies for better control of the occurrence, growth, or survival of this organism in foods. An additional publication on non-O157 serotype strains is in preparation.


Last Modified: 10/21/2014
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