Synergistic Antimicrobial Effects of Organic Acids in Combination with Carvacrol Against Shigella Sonnei

This study aimed to investigate the antimicrobial activities of organic acids, carvacrol and their combination against Shigella sonnei. Shigella sonnei at a density of approximately 7.4 log cfu/mL in tryptic soy broth (TSB) was barely inactivated by 0.5% w/v acetic or citric acid; however, the number of S. sonnei were reduced to 4.53 and 3.25 log cfu/mL by 0.5% w/v malic and lactic acid, respectively, after the treatment for 9 h. Shigella sonnei was completely inactivated by 0.02 and 0.03% w/v carvacrol within 70 and 20 min, respectively. Furthermore, the treatment with the combination of 0.5% w/v lactic acid and 0.02% w/v carvacrol completely inactivate S. sonnei at 6.52 log cfu/mL in TSB within 10 min. The number of S. sonnei inactivated by the combination was greater than the sum of those inactivated by 0.5% w/v lactic acid and 0.02% w/v carvacrol, indicating the synergistic effect of the combination. Practical ApplicationsThe synergistic inactivation against Shigella sonnei by the combination of an organic acid and carvacrol demonstrated in this study is directly applicable to fresh food processing, and these findings could be useful for the development of new means to keep food safety from S. sonnei infection.