Lamiaceae essential oils and alcoholic extracts and their effects on zoonotic multi rug- resistant bacteria

Abstract

In the last decade, an increasing incidence of multi-drug resistant bacterial strains, both in human and animal medicine, has been reported. Furthermore, the phenomenon of drug resistance was encountered mainly in zoonotic bacteria. Vegetal extracts and essential oils, widely used in folk medicine and well-known for their bioactive potential, were suggested by numerous researches to represent a therapeutic alternative. It is only recently that a number of findings have emerged on the chemistry and biological activity of plants in Lamiaceae family, some of them referring to bioactive compounds able to inhibit bacterial growth [1,2]. This study aimed to evaluate and compare antimicrobial properties of essential oils and ethanolic extracts from Thymus vulgaris, Salvia officinalis, Lavandula officinalis, Mentha piperita, Rosmarinus officinalis, Ocimum basilicum, Melissa officinalis and Origanum vulgare against multidrug-resistant strains of Staphylococcus spp., Salmonella spp., E. coli and Pseudomonas aeruginosa, isolated from diseased animals. The antimicrobial potential was assessed by disc diffusion test, while minimal inhibitory (MIC) and bactericidal (MBC) concentrations were determined by a broth microdilution method. Synergistic interactions between the tested extracts and two antibiotics (enrofloxacin and amoxicillin-clavulanic acid) were screened by Etest method. The antibacterial effects, dependent on type of vegetal product and on bacterial species, were statistically significant (p<0.001–0.05) for all screened Lamiaceae species, more pronounced against Gram-positive than Gram-negative bacteria. Melissa officinalis essential oils demonstrated the strongest antimicrobial efficacy against all bacterial strains. Thymus vulgaris and Salvia officinalis essential oils possessed promising antibacterial properties against tested animal pathogens, displaying synergism with enrofloxacin.