Purpose: This research was conducted to gain a better understanding of the GAD system, which would allow more effective control of pathogens. By interfering with the GAD system, it may be possible to decrease acid resistance in several food pathogens, which would allow a more targeted approach to the reduction of specific foodborne pathogens.
Methods: A number of dicarboxylic acids and their salts were tested for their antimicrobial properties, in terms of survival, with two organisms Escherichia coli K12 and Listeria monocytogenes 10403S. In addition, mutants of the GAD system were used to assess the role of selected acids on the GAD system under acidic conditions. The effectiveness of the acids was determined by examining levels of gamma aminobutyric acid (GABA), the byproduct of the GAD system, using enzymatic assay methods in combination with gas chromatography.
Results: Of the compounds tested, sodium fumarate (SF), was shown to be the most active. Under acid conditions, its presence resulted in L. monocytogenes reductions up to four logs (8.6 mM). For E. coli, FS achieved a reduction of up to two logs (10 mM). Analysis of GAD system byproducts indicated that the presence of SF had a significant impact on the GAD system. A significant difference was noted in the extracellular levels of GABA produced by both organisms. A significant decrease in GABA was found in E. coli and a significant increase in L. monocytogenes (paired student T-test; P value <0.05).
Significance: Developing more targeted methods for disrupting the acid protection mechanisms in foodborne organisms could result in their efficient elimination from food.