Inhibitory effect of organic acids against Enterobacter sakazakii in laboratory media and liquid foods

Enterobacter sakazakii is an emerging foodborne pathogen that causes neonatal meningitis and sepsis, with mortality rates of 40–80%. This study was conducted to determine the effect of organic acids on inhibiting the survival and the growth of E. sakazakii in laboratory media and several liquid foods. Inhibitory effects and the minimum inhibitory concentration (MIC) of nine acids (hydrochloric, lactic, malic, formic, phosphoric, propionic, citric, tartaric, and acetic acid) against E. sakazakii were determined by the agar disc diffusion test and broth dilution methods. Out of nine acids tested, five acids (malic, formic, propionic, citric, and acetic acid) showed antibacterial activity against one or more E. sakazakii stains. And, propionic and acetic acid were found to be the most effective with the lowest MIC values of 16–31 and 31–63 mM against E. sakazakii, respectively. Therefore, these two acids were selected for further testing in liquid foods (Sun-Sik, baby food, grape juice and apple juice). Regarding foods tested, grape juice itself has an inhibitory effect and reduced or maintained levels of E. sakazakii during storage. However, 10 mM of propionic and acetic acid in Sun-Sik and apple juice, and 100 mM of propionic and acetic acid in baby foods were necessary to eliminate E. sakazakii in each food type, respectively. These results suggest that organic acids such as propionic and acetic acid may possibly be used as preservatives to inhibit E. sakazakii in liquid foods.