Marked Synergistic Bactericidal Effects and Mode of Action of Medium-Chain Fatty Acids in Combination with Organic Acids against Escherichia coli O157:H7

Abstract

The aim of this study was to examine the synergistic bactericidal effects of medium-chain fatty acids (MCFAs; caprylic, capric, and lauric acid) and organic acids (OAs; acetic, lactic, malic, and citric acid) against Escherichia coli O157:H7 and to identify their underlying mechanism(s) of action. E. coli O157:H7 was treated with MCFAs, OAs, or different combinations of MCFAs and OAs. Membrane damage and cell morphology were examined by flow cytometry and transmission electron microscopy, respectively. Combined treatment resulted in an additional log-unit reduction compared with the sum of the reductions obtained after individual treatment. For example, caprylic acid (1.0 mM, or 0.016%) and citric acid (1.0 mM, or 0.012%) alone showed negligible bactericidal effects (0.30-and 0.06-log-unit reductions, respectively); however, a marked synergistic effect (>7.15-logunit reduction) was observed when the two were combined. Although flow cytometry and microscopic analyses of bacteria treated with individual MCFAs and OAs showed evidence of membrane disruption, the bacteria were still able to form colonies; thus, the cell damage was recoverable. In contrast, cells exposed to combined treatments showed clear membrane disintegration and/or cell death (irreversible damage). The mechanism underlying the antimicrobial effects of combined treatment with MCFAs or OAs may involve disruption of the bacterial membrane, which then facilitates the entry of other antimicrobial compounds into the cytoplasm. The main advantage of combined treatment with very low concentrations of natural antimicrobial compounds is that it is very cost-effective. Thus, this approach may be an alternative to more conventional antimicrobial treatments, such as those currently used in public health, medical centers, and the food industry.

Enhanced bactericidal action of acidified sodium chlorite caused by the saturation of reactants

“…Thus, researchers, food manufacturers, food managers and consumers are interested in increasing the effectiveness of antimicrobials while reducing their level of usage (Valero and Frances ; Pei et al . ; Kim and Rhee ; Ye et al . ).…”

“…However, modern consumers tend to be very concerned about the presence of potential chemical risks in the food chain, which can be caused by the persistence of residual toxic compounds in processed foods (Kher et al 2013). Thus, researchers, food manufacturers, food managers and consumers are interested in increasing the effectiveness of antimicrobials while reducing their level of usage (Valero and Frances 2006;Pei et al 2009;Kim and Rhee 2013;Ye et al 2013).…”

Physical and Chemical Methods for the Reduction of Biological Hazards in Animal Feeds

“…Meanwhile, medium chain fatty acids, such as capric and caprylic acid, have been shown to be effective against E. coli and Salmonella growth (Kim and Rhee, 2013). Caprylic acid added to feed has been shown to decrease the quantity of Salmonella colonization in broiler chicks (Johny et al, 2009).…”

Effect of dietary supplemental medium chain fatty acids instead of antibiotics on the growth performance, digestibility and blood profiles in growing pigs

“…Many people thought that selected multiple products that can work synergistically even that a comprehensive system is a potential solution (Aarestrup, ; Allen, Levine, Looft, Bandrick, & Casey, ; Seal, Lillehoj, Donovan, & Gay, ). Some natural antimicrobials such as medium‐chain fatty acids, essential oils and organic acids are considered alternates (Kim & Rhee, ). In this paper, we focus on study effects of MCFA alternatives to CSP (Chlortetracycline, sulphonamide dimethazine and procaine penicillin, 1:1:1) in pigs.…”