Antibacterial effect of Satureja hortensis and Salvia officinalis essential oils against major bovine mastitis bacteria

Treatment of bacterial diseases such as bovine mastitis with antibiotics has problems such as antibiotic resistance and drug residue in animal products.  Essential oil of medicinal plants have antibacterial activity and are suitable alternatives. This study examined the antimicrobial activity of Salvia officinalis (sage) and Satureja hortensis (savory) essential oils on major mastitis-causing bacteria, including Staphylococcus aureus, Streptococcus agalactiae, and Escherichia coli. Chemical compositions of essential oils were determined by gas chromatography-mass spectrometry. Minimum inhibitory concentration and minimum bactericidal concentration of oils were determined with serial broth dilution method using autoclaved whole milk rather than synthetic broth. The effect of sub-minimum inhibitory concentrations of essential oils on the growth curve of tested bacteria in milk was obtained in 0, 1, 2, 4, 10, and 24 hours. Major compositions of sage and savory essential oils were carvacrol (61.01%), thymol (20.41%), 1R-α-pinene (7.88%), eucalyptol (32.45%), thymol (28.24%), and α-pinene (13.42%), respectively. The minimum inhibitory concentration and minimum bactericidal concentration ranged 1.25-2.5% and 2.5-5% for savory, and 0.625-1.25% and 1.25-2.5% for sage, respectively. Savory and sage significantly decreased the S. aureus and S. agalactiae population in 4, 10, and 24 h (p < 0.05) and E. coli population in 10 and 24 h (p = 0.01). The sage and savory essential oils had antibacterial effects against three tested bacteria, and sage had a stronger effect than savory because of stronger antibacterial components (carvacrol and thymol). Further in vivo tests are recommended to evaluate the efficiency of these essential oils on the treatment of bovine mastitis.