Effect of Lavandula stoechas (Lavender) and Origanum majorana (Marjoram) oils on major mastitis-causing bacteria in vitro

Treatment of bacterial diseases with antibiotics has problems such as antibiotic resistance and side effects. Essential oils of medicinal plants have antibacterial effect and are suitable alternatives. Lavandula stoechas and Origanum majorana are two members of lamiaceae family that have shown antibacterial effect against some bacteria. Escherichia coli, Staphylococcus aureus, and Streptococcus agalactiae bacteria are major bovine mastitis-causing bacteria. Therefore, this study examined the antimicrobial activity of Lavandula stoechas (lavender) and Origanum majorana (marjoram) essential oil against these bacteria in comparison with gentamycin and amoxicillin/clavulanate antibiotics.

Chemical compositions of essential oils were determined by GC/MS. Broth dilution testing using macrodilution was performed to determine minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of essential oils and licospectinomycin as positive control and the inhibition zones of oils, gentamycin and amoxicillin/clavulanate antibiotics were assayed by disk diffusion method. The effect of sub-MIC concentrations of essential oils on tested bacterial count was obtained at 0, 6, 10 and 24 hours and growth curve were plotted as log cfu/ml.

Main components of the Lavandula stoechas and Origanum majorana oils were 17-pentatriacontene (42.15%), linalyl acetate (26.82%), eucalyptol (18.87%), linalool (5.7%) and 3-cyclohexene-1-ol,4-methyl-1-(1-methylethyl)-,(R)-(44.84%), α-terpineol (6.83%), P-cymene (6.75%), respectively. MIC and MBC values ranged from 0.15 - 0.62% for lavender and 0.62 - 1.25% for marjoram. MIC and MBC of licospectinomycin antibiotic were 0.07 - 0.31% and 0.15 - 0.64%, respectively. The lavender and marjoram essential oils had the most effective against S. aureus and MIC and MBC values were 0.15% and 0.31%, respectively. Also, the most effective of Lincospectinomycin antibiotic was against S. aureus and MIC and MBC values were 0.07% and 0.15%, respectively. The Lavandula stoechas and Origanum majorana oils at sub-MIC concentrations significantly reduced the bacterial population at 24 h. The inhibition zone of lavender and marjoram essential oils had no significant difference against S. aureus with gentamycin and amoxicillin/clavulanate antibiotics and against E. coli with gentamycin but against S. agalactiae were significantly lower than gentamycin and amoxicillin/clavulanate.

Essential oils of Lavandula stoechas and Origanum majorana had antibacterial activity against Staphylococcus aureus, Streptococcus agalactiae and Escherichia coli bacteria in vitro. This effect had no significant difference against S. aureus with gentamycin and amoxicillin/clavulanate and against E. coli with gentamycin that show satisfactory effects of oils. Clinical studies on therapeutic effects of Lavandula stoechas and Origanum majorana oils on different diseases such as bovine mastitis are recommended.