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United States Department of Agriculture

Agricultural Research Service

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Research Project: FOOD SAFETY AND FOOD SECURITY ISSUES ASSOCIATED WITH ACID AND ACIDIFIED FOODS

Location: Food Science Research

2007 Annual Report


1a.Objectives (from AD-416)
The overall objective of this research is to develop methods to prevent the growth of pathogenic and spoilage microorganisms in minimally preserved, brined, and fresh-cut foods and optimizing safety, quality, and sensory attributes specifically through:.
1)development of fundamental knowledge of the biochemistry of bacterial adaptation to acidified environments;.
2)determination, through analysis of gene/protein expression profiles, the responses to intrinsic and extrinsic stressors and, in particular, the effect of oxygen imposed on pathogenic bacteria during production, processing, and storage of acid and acidified foods;.
3)development of data and its use for the development of mechanistic models for growth, survival and inactivation of pathogens.


1b.Approach (from AD-416)
The effect of common food acids and acid preservatives will be evaluated for their relative ability to enhance killing of acid-tolerant food pathogens, particularly Escherichia coli O157:H7, in the absence of oxygen and independent of pH. Work will be carried out at biosafety level 2 (BSL-2) due to the organisms under investigation. Selected acid/pathogen strain combinations will be analyzed using genetic and biochemical analyses to determine the mechanisms by which acids are responsible for killing E. coli and other pathogens. This information will be utilized to identify common metabolic targets for the killing effects of acids and acid preservatives, as well metabolic targets unique to particular acids. Since we have found that oxygen increases the killing rates of acid-tolerant pathogens at low pH, similar investigations will be done to determine the genetic and metabolic responses of acid-tolerant pathogens to acids in the presence of molecular oxygen and oxygen radicals. These results will be used to determine the mechanisms by which oxygen species enhance killing of pathogens in acid and acidified foods. Data from genetic and metabolic experiments will be used to develop mechanistic mathematical models and validate the models that are developed in order to test hypotheses developed from genetic and metabolic investigations of acid-killing and acid resistance of food pathogens.


4.Accomplishments
Use of DNA binding dyes to selectively identify live cells of pathogenic bacteria

Selected DNA binding dyes were used to develop methods for a quantitative DNA amplification assay to determine the number of live bacteria in the presence of dead cells. The assay works without having to culture the bacterial cells to determine a count of only the live cells, not dead cells. While these types of assays were previously known in the scientific literature, we determined how the assay can be used for cells in broth or from bacteria obtained from a film on a surface such as stainless steel. Using this method, a count can be determined of only the live bacterial cells in a bacterial culture that is undergoing acid or other kinds of stresses. These types of non-culture based procedures are important to use because when working with stressed populations of bacteria, injured cells can not always be recovered by traditional bacterial agar Petri plate counting methods. These assays can also be used to specifically identify and enumerate subpopulations of bacteria in mixed culture without plating. The research addresses the Food Safety National Program, specifically Problem Statements 1.2.4, Processing Intervention Strategies, and 1.2.9, Food Security in the 2006-2010 NP 108 Action Plan.


6.Technology Transfer

Number of non-peer reviewed presentations and proceedings4

Review Publications
Pan Y, Breidt F, Kathariou S. 2006. Resistance of Listeria monocytogenes in biofilms to sanitizing agents and starvation in a simulated food processing environment. Appl Environ Microbiol 72 (12):7711-7717

Last Modified: 8/30/2014
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