|ROMICK, THOMAS - NCSU
Submitted to: Journal of Applied Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/9/1997
Publication Date: N/A
Interpretive Summary: Listeria monocytogenes is a bacterium that has caused poisoning outbreaks in various foods, including meat, dairy, and vegetable products. We are studying ways to prevent growth and survival of this bacterium in non-acidified or mildly acidified, pickled vegetables. We found that the bacterium produces a somewhat unique compound, acetoin, when it grows in the presence but not in the absence of oxygen. We used acetoin production as an indicator of L. monocytogenes growth and studied how certain types of acids and preservatives can be used to prevent growth of this food pathogen. The method can be used to screen inhibitors of its growth for possible application in the food industry.
Technical Abstract: It has been shown that Listeria monocytogenes produces acetoin from glucose under aerobic conditions. A defined medium with glucose as the sole carbon source was used in an aerobic shake flask culture to reliably produce acetoin. Acetoin, the reactive compound in the Voges-Proskauer test, was assayable in the medium and was used to quantify the metabolic response when inhibitors were added to the medium. Inhibitors such as lactic, acetic, propionic, and benzoic acids were used to demonstrate the utility of acetoin production as an indicator of metabolic disruption. With increasing levels of inhibitor, the metabolic and growth responses were measured by acetoin production and optical density change, respectively. Both measurements decreased in a similar manner with increasing inhibitor concentrations. The data also showed the apparent mode of action of the inhibitors. A bacteriostatic effect was observed for the protonated organic acids, acetic and propionic, whereas protonated lactic and benzoic acids gave an irreversible (apparent bacteriocidal) effect. Lactic, acetic and propionic acids showed stimulation of metabolic activity at low concentrations, but benzoic did not. Acetoin production is a novel method for quantifying and assessing the mode of action of inhibitors against L. monocytogenes. This system can be used to screen inhibitors for applications in food safety.