Abstract

This work investigates the activities of nisin and gallic acid, used either alone or in combination, against Listeria monocytogenes Scott A Cm^rEm^r. The antimicrobial activity was determined using agar diffusion tests. The growth profile was evaluated by measurements of optical density and the numbers of viable cells. Lipid peroxidation was measured by the thiobarbituric acid-reactive substances (TBARS) technique, and the levels of reduced glutathione (GSH) were determined by the 5,5-dithio-bis-2-nitrobenzoic acid (DTNB) method. Growth of the pathogen was inhibited by the combined use of nisin and gallic acid, with an inhibition zone of approximately 11 mm at concentrations of 8 mg/ml and 100 IU/ml, respectively. No significant reduction in the number of viable pathogen cells was observed after 18 hours of exposure to nisin and gallic acid. There was a significant increase in the GSH concentration, and a decrease in lipid peroxidation, when the pathogen was exposed to increasing concentrations of nisin and gallic acid, used either alone or in combination, for a period of 18 hours. It was concluded that the Listeria monocytogenes cell line studied was able to resist the action of oxidizing agents by increasing the synthesis of GSH.

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