In vitro antimicrobial activity of natural substances convenient for use in animal breeding instead of antibiotics

Abstract

The increasing antibiotic resistance of microbial pathogens isolated from farm animals tissues and the environment has been the one of the most important challenges associated with the use of antibiotics. In order to achieve better production on a farm, animal feed is enriched with antibiotics often originally intended for therapeutic purposes, which may lead to notable increases in microbial resistance. One possible approach to decreasing the excessive use of antibiotics in livestock as well as antimicrobial resistance is utilizing the antimicrobial properties of natural substances. The aim of this study was to evaluate the antimicrobial activity of natural substances including carvacrol, thymol, eugenol, gallic acid, octyl gallate, cnicin and usnic acid against a wide spectrum of microorganisms. Cnicin was the only compound which was isolated from the plant with use of column chromatography. The antimicrobial activities of these natural substances were determined on the basis of their minimum inhibitory, minimum bactericidal and minimum fungicidal concentrations using the microdilution method. This determination of antimicrobial activity revealed thymol and cnicin to be effective natural substances against all tested microorganisms. Octyl gallate had a strong inhibitory and bactericidal effect against gram-positive bacteria and was the most effective against Candida strains. Usnic acid was shown to have the lowest minimum inhibitory concentrations for gram-positive bacteria. These results suggest the possible incorporation of natural substances in animal rearing in order to reduce the high amount of antibiotics which are not used directly to treat animal diseases.