Antibacterial Effect of Eight Essential Oils against Bacteria Implicated in Bovine Mastitis and Characterization of Primary Action Mode of Essential Oil.

During the current investigation, eight essential oils (EOs) were tested for their antimicrobial activity against six species, belonging to the genus of , multi-resistant to antibiotics (, , , , , ), three methicillin-resistant strains (MRSA) and two strains of producing extended-spectrum β-lactamase (ESBL) responsible for bovine mastitis. Our results indicated that the antimicrobial activities of eight EOs varied significantly among the types of EOs and bacterial species. and EOs display important antibacterial activity against all tested strains, with the inhibition zone diameters situated between 20 and 45 mm, while EOs of , , , and exerted an intermediate activity. For , this effect depends on bacteria species. In fact, an important effect was observed against , , , and MRSA (EC 39+) strains. In addition, the important lytic effect was observed against MRSA strains, showing that Gram-positive bacteria were more sensitive to EO than Gram-negative ones. Concerning the characterization of the mode action of , experiments of kill-time, bacteriolytic, loss of salt tolerance and loss of cytoplasmic material showed that the used EO was able to destroy cell walls and membranes followed by the loss of vital intracellular materials. In addition, it inhibits the normal synthesis of DNA, causing the bacterial death of and MRSA strains. This study shows the potential of using of EOs, particularly to inhibit the growth of Gram-positive and Gram-negative bacteria multi-resistant to antibiotics causing bovine mastitis.