Comparison of bacteriostatic and bactericidal activity of 13 essential oils against strains with varying sensitivity to antibiotics

Aims: To compare the bacteriostatic and bactericidal activity of 13 chemotyped essential oils (EO) on 65 bacteria with varying sensitivity to antibiotics. Methods and Results: Fifty-five bacterial strains were tested with two methods used for evaluation of antimicrobial activity (CLSI recommendations): the agar dilution method and the time-killing curve method. EO containing aldehydes (Cinnamomum verum bark and Cymbopogon citratus), phenols (Origanum compactum, Trachyspermum ammi, Thymus satureioides, Eugenia caryophyllus and Cinnamomum verum leaf) showed the highest antimicrobial activity with minimum inhibitory concentration (MIC) < 2% (v/v) against all strains except Pseudomonas aeruginosa. Alcohol-based EO (Melaleuca alternifolia, Cymbopogon martinii and Lavandula angustifolia) exhibited varying degrees of activity depending on Gram status. EO containing 1.8-cineole and hydrocarbons (Eucalyptus globulus, Melaleuca cajeputii and Citrus sinensis) had MIC90% >= 10% (v/v). Against P. aeruginosa, only C. verum bark and O. compactum presented MIC <= 2% (v/v). Cinnamomum verum bark, O. compactum, T. satureioides, C. verum leaf and M. alternifolia were bactericidal against Staphylococcus aureus and Escherichia coli at concentrations ranging from to 0.31% to 10% (v/v) after 1 h of contact. Cinnamomum verum bark and O. compactum were bactericidal against P. aeruginosa within 5 min at concentrations < 2% (v/v). Conclusions: Cinnamomum verum bark had the highest antimicrobial activity, particularly against resistant strains. Significance and Impact of the Study: Bacteriostatic and bactericidal activity of EO on nosocomial antibiotic-resistant strains.