Antimicrobial properties of essential oils - animal health aspects

The spread of antimicrobial resistance is a growing public and animal health problem worldwide. In animal health industry, especially in livestock management the use of antibiotics for non-therapeutic purposes, mainly as prophylaxis and metaphylaxis can contribute to the increase of antibiotic resistance despite the number of regulations introduced. In line with the One Health approach, attention is increasingly turning to alternative solutions to decrease the consumption of antimicrobial drugs. One of the main areas of interest is the antimicrobial potency of essential oils extracted from medicinal plants, that can replace the use of antibiotics. Medicinal plants have been used for thousands of years; however, the exact composition and mechanism of action in microorganisms of essential oils derived from these plants are difficult to research. Despite these difficulties studies has shown promising results both in vitro and in vivo experiments. In addition, the synergistic or additive effect of essential oils when used in combination with antibiotics is now scientifically proven. In this literature review, the authors describe the antimicrobial efficacy of individual medicinal plants and essential oils extracted from them. This review focuses on the antimicrobial resistance and use of antibiotics in livestock especially in poultry. Different methods are described of evaluating the effectiveness of essential oils in vitro and in vivo studies including their potency against bacteria and biofilm, viruses and fungi, using diffusion or dilution methods under laboratory conditions and their effect on ileal microbiota, feed intake, daily gain weight, feed conversion ratio, mortality, blood cell profile, etc. under on-site conditions.