FACTORS THAT INTERACT WITH THE ANTIBACTERIAL ACTION OF THYME ESSENTIAL OIL AND ITS ACTIVE CONSTITUENTS

The viable counts of Salmonella typhimurium on nutrient agar (NA) decr eased upon the addition of either the essential oil of thyme or its co nstituent thymol, especially under anaerobic conditions. Antagonistic effects of thymol against Staphylococcus aureus were also greater unde r anaerobic conditions. In contrast to the phenolic constituents of th e oil, thymol and carvacrol, the chemically related terpenes p-cymene and gamma-terpinene had no antagonistic effects against Salm. typhimur ium. The addition of Desferal to NA counteracted the antibacterial eff ects of both thyme oil and thymol. No support was obtained, however, f or a possible role of iron in the oxygen-related antibacterial action of the thyme oil and thymol or for the observed effect of Desferal. In the presence of thymol, the viable counts of Salm. typhimurium obtain ed on a minimal medium (MM) were lower than those obtained on NA. Addi tion of bovine serum albumin (BSA) neutralized the antibacterial actio n of thymol. It is suggested that the effects of BSA or Desferal are d ue to their ability to bind phenolic compounds through their amino and hydroxylamine groups, respectively, thus preventing complexation reac tions between the oil phenolic constituents and bacterial membrane pro teins. This hypothesis is supported by the marked decrease in the viab le counts of Salm. typhimurium caused by either thyme oil or thymol wh en the pH of the medium was changed from 6.5 to 5.5 or the concentrati on of Tween 80 in the medium was reduced.