Formulations of essential oils obtained from plants traditionally used as condiments or traditional medicine active against Staphylococcus aureus isolated from dairy cows with mastitis

The prophylactic and therapeutic overuse of antimicrobials on the farm has contributed to the emergence of hard-to-fight bacterial strains causing bovine mastitis. Aiming at alternative therapies, this study evaluated the antimicrobial activity of 20 essential oils against clinical Staphylococcus aureus strains. Of them, five with strong activities were selected and evaluated for their minimum inhibitory concentrations (MIC) in culture medium and milk, cytotoxicity against bovine mammary cells (MAC-T), antiadhesive properties, and interactions among themselves and with cefoperazone. The oils remained active on milk, were not cytotoxic, and some concentrations stimulated MAC-T cells growth, suggesting healing potential. Subinhibitory concentrations of Coriandrum sativum, Origanum vulgare, Syzygium aromaticum, and Thymus vulgaris reduced biofilm formation by at least 80%. Several oil and cefoperazone combinations displayed additive interaction, with O. vulgare and C. sativum showing the most promising results. We developed formulations for being used as prophylactic postdipping solutions in the field, containing different concentrations (1% or 3%) of the active oils, alone or in combination, with 3% glycerin, 1% Tween 80, and water. The formulations showed strong antimicrobial activity in milk and enhanced antiadhesive properties, specially when two oils were combined in the formula, indicating promising biotechnological and therapeutical applications.