The Chemical Composition and Antibacterial Effect of Essential Oils of Rosemary and Basil in Milk

Background: According to the diverse side effects of antibiotics, new and natural antibacterial substances are needed to treat bacterial diseases, and one of these substances is the essential oils (EOs) of medicinal plants. Milk fat and protein may reduce the antimicrobial impact of EOs. Objectives: This study aims to investigate the antibacterial activity of rosemary and basil EOs compared to lincospectinomycin antibiotic against three mastitis-causing bacteria, Streptococcus agalactiae, Staphylococcus aureus, and Escherichia coli in milk media. Methods: Chemical compounds in EOs were identified by gas chromatography. The minimum bactericidal concentration (MBC) and minimum inhibitory concentration (MIC) of EOs were studied using the tube dilution method, and the growth curve of bacteria was studied at 0, 6, 10, and 24 h. Results: The most crucial rosemary compounds were carene (45.11%) and eucalyptus (20.62%), and those of basil were estragol (70.42%) and carene (17.99%). The MIC and MBC of rosemary were lower than those of lincospectinomycin, and those of basil were similar to those of lincospectinomycin. At 6-h, the bacterial reduction of E. coli and S. agalactiae was significant, and the population reduction of rosemary was significant for S. aureus. At 24 h, rosemary and basil significantly diminished the bacterial count of S. aureus, and basil significantly decreased the S. agalactiae count. Conclusion: The antibacterial effects of EOs are acceptable, and clinical studies are recommended to treat other diseases, including mastitis.