2012 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 related to in-house objective 1, to assure a 5-log reduction in acid tolerant pathogens. This research was done to determine the extent of Escherichia coli O157:H7 acid tolerance. 50 or more non-O157:H7 E. coli serotype pathogenic strains were obtained with ARS collaborators, and examined with a non-ARS collaborator’s help to determine acid resistance. In general, the results showed that the non-O157 serotype strains were more acid resistant than many O157:H7 serotype strains. The results will be used to select strain pairs of bacteria for resistance comparisons, to further the research on how acid resistance affects the metabolism and internal physiology of these pathogenic bacteria.