In vitro antibacterial activity of essential oils from plant family Lamiaceae

Medicinal plants and herbs have been used for many years in treating various animal and human diseases. Secondary metabolites from medicinal plants are widely unexploited in 'conventional' animal production systems. The aim of the investigation was to study antimicrobial activities of three essential oils on five bacterial species (Escherichia coli. Salmonella choleraeszus, Proteus mirabilis, Staphylococcus aureus. Enterococcus faecalis) obtained from the American Type Culture Collection The plants used in this study were oregano (Origanum vulgare L.), thyme (Thymus vulgaris L.) and wild thyme (Thymus serpyllum L.), all members of Lamiaceae family. The antibacterial activity of essential oils was tested by disc diffusion method and broth micro-dilution susceptibility assay, according to the National Committee for Clinical Laboratory Standards Guidelines. All the tested oils demonstrated antimicrobial activity on used bacterial strains. The analysis of variance revealed that there were highly significant differences (P < 1%) between the effects of essential oils, concentrations and interactions of essential oils within all tested groups of bacteria. The strongest antibacterial effect was shown by oregano essential oil, while the oil extracted from wild thyme was least potent. The antibacterial activity of essential oils declined with decreasing concentration, regardless of the tested bacteria. Antibacterial effects of essential oils showed by broth micro-dilution method are in accordance with the results of a preliminary screening performed by the disc diffusion method