Defining the Minimum Inhibitory Concentration of Synthetic and Commercial Medium Chain Fatty Acid Based Products Against Salmonella Typhimurium

Research has confirmed that a 2% inclusion rate of a blend of C6:0, C8:0, and C10:0 in swine diets and ingredients can reduce Salmonella enterica serotype Typhimurium. However, it is unclear how the chain length and concentration of medium chain fatty acids (MCFA) impacts bacteriostatic properties. This can be tested through a minimum inhibitory concentration (MIC) benchtop assay, which identifies the lowest concentration of a chemical that prevents visible growth of a bacterium. The objective of this set of experiments was to utilize MIC as a mechanism to screen commercial or developmental feed additives containing MCFA for potential to mitigate Salmonella Typhimurium. First, the MIC of four synthetic MCFA treatments (C6:0, C8:0, C10:0, and 1:1:1 ratio of C:6:C8:C10 blend) was determined for Salmonella Typhimurium. The MIC of each treatment was conducted in a modified microbroth dilution and had three replicates. The MIC of C6:0 and C8:0 (0.4 and 0.5%, respectively) were similar (P > 0.05) to one another, but lower (P < 0.05) than the MIC of C10:0 or the blend of C6:C8:C10 (0.6% and >1.0%, respectively). It was therefore hypothesized that products containing high concentrations of C6:0 or C8:0 would have the greatest potential to mitigate Salmonella Typhimurium. Next, the fatty acid profile of 24 feed additive products that were commercially developed or in the development process and containing MCFA was determined via gas chromatography. As a result, four products in the development phase from varying companies plus coconut oil were selected as having a high potential for mitigating Salmonella Typhimurium based on their C6:0 and C8:0 levels. Development products 1, 2, 3, 4, and coconut oil contained 29.5, 43.1, 27.4, 0.98, and 6.82 mg/g of C6:0 and 123.20, 610.3, 248.7, 227.1, and 72.0 mg/g of C8:0, respectively. The MIC of these products vs. Salmonella Typhimurium was then determined. The MIC of Product 1 and Product 2 (0.5% and 1.3%, respectively) were similar (P > 0.05) to one another, but lower (P < 0.05) than the MIC of Products 3 or 4 (3.8% and 4.3%, respectively). All four products had a lower (P < 0.05) MIC than coconut oil (> 5.0%). In summary, current or future feed additives containing high concentrations of C6:0 and C8:0 appear to be more effective at mitigating Salmonella Typhimurium than those containing C10:0. Furthermore, it is hypothesized that free MCFA have greater antibacterial potential than those in triglyceride form.