Background: Organic acids (e.g. acetic and lactic acid) have been used in foods as natural preservatives. Acetic acid and its salts are used in foods as antimicrobial and acidulant agents. The aim of this study was to evaluate the antibacterial activity of acetic and lactic acids against the Listeria monocytogenes. Materials and Methods: This experimental study was conducted at the Department of Food Hygiene (Faculty of Veterinary Medicine, Urmia University) during autumn 2015. The antibacterial effects of acetic and lactic acid against Listeria monocytogenes were determined using minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC) and cell constituents release methods. The concentration ranges of acetic and lactic acid (0.0195-10 and 0.043-22.2 μl/ml, respectively) were used to determine the MIC of acids. Results: Based on the results, acetic and lactic acid inhibited the growth of Listeria monocytogenes and acetic acid had stronger effect against the the bacterium. The MIC values for acetic acid and lactic acid were 2.5 and 5 μl/ml, respectively. Cell constituents release showed that acetic and lactic acids are able to lyze the bacterial cell. Conclusion: Acetic and lactic acids were effective in inhibiting the growth of Listeria monocytogenes and the antibacterial effect of acetic acid was stronger than that lactic acid. These acids can be used in foods in combination with other preservatives to inhibit the food borne pathogens and food spoilage microorganisms
