ENTEROCOCCI AND THEIR RESISTANCE TO ANTIBIOTICS AND THYME ESSENTIAL OIL

Abstract

Enterococci are important part of microflora of food animal origin. They have positive (probiotic effect, production flavor compounds during food ripening) and also negative (production biogenic amine, antibiotic resistance, biofilm production) properties. The aim of this work was to determine resistance to different concentrations of thyme essential oil and antibiotic resistance of enterococci isolated from pork (n=3) and poultry (n=17). The antibiotic resistance of isolates was determined by disc diffusion method and the antibacterial effect of thyme essential oil was assayed by a microdilution method in 96-well microtitration plates after determination of absorbance at 630 nm (A630). Of 20 tested enterococci, 85 % were resistant to tetracycline, 35 % to erythromycin, 15 % to ampicillin and 5 % to gentamicin. No resistance to vancomycin was detected. All tested strains of enterococci were able to grow and reproduce at concentrations of thyme essential oil 0.033 % and 0.066 %. Inhibitory effect of thyme essential oil began at a concentration of 0.099 %, but only for 10 % of the tested strains. Even the highest concentration tested thyme essential oil 0.166 % did not inhibit all the tested strains, because 25 % of enterococcal strains continued to grow. No correlation between antibiotic resistance and resistance to the thyme essential oil was detected for tested enterococci. The thyme essential oil has potential for using in food industry to inhibit spoilage or pathogenic microorganisms, but it is necessary to test antimicrobial activity in other in vitro and in vivo experiments and also in experiments with impact on the sensory properties of food.