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ARS Home » Southeast Area » Raleigh, North Carolina » Food Science Research » Research » Research Project #414433


Location: Food Science Research

2009 Annual Report

1a. Objectives (from AD-416)
The purpose of this study is to determine the survivability of Escherichia coli O157:H7 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 E. coli O157:H7 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 relates to inhouse objective 3: Development of data and its use for the development of mechanistic models for growth, survival and inactivation of pathogens. The safety of acidified foods is of concern to FDA and producers of these products. Some disease causing bacteria are very acid resistant and can survive for up to several months in some acidified foods such as cucumber pickle products, if these foods are not properly treated. Bacterial strains of a common acid resistant organism Escherichia coli O157:H7 were analyzed to determine how they survive under conditions of acidified foods. It was found that survival and acid resistance varied depending on source of isolation of the strain. Strains isolated directly from animal sources were more acid resistant than strains isolated from foods or human disease. Cooperative research to determine how bacterial strains alter acid resistance with continuous growth on laboratory media were carried out. Disease causing bacteria isolated from foods, animal manure, water and other sources (Escherichia coli O157:H7) were previously found to vary in acid resistance depending on the source of isolation for the strains. Bacterial strains were used that were previously sent to Kangwon University, South Korea, for collaborative research. It was found that the variation in acid resistance of these strains was not due to repeated growth on laboratory media. Progress was monitored by emails, phone calls and site visits.

4. Accomplishments