Antibacterial efficacy of essential oil spray formulation for post-milking disinfection in dairy cows.

Abstract

Mastitis is an essential issue in dairy cows. Post-milking teat dips can help reduce this problem, but they employ harsh disinfectants, and many bacteria are becoming increasingly tolerant. This study aimed to investigate the antibacterial activity of clove, citronella, and sweet basil essential oils against the common bovine mastitis causative agents Staphylococcus aureus, Streptococcus agalactiae, and Escherichia coli and to develop an antiseptic post-milking teat spray for use in dairy cows. The in vitro antimicrobial activity of the essential oils was determined by broth microdilution and time-kill assays. Essential oil-based post-milking teat sprays were developed. The bacterial eradication efficacy of the formulations was determined by time-kill assays and their stability was tested by repeated freeze-thaw cycles. The most effective formulation was tested in dairy cows. The minimum inhibitory concentrations and minimum bactericidal concentrations of the tested essential oils against S. aureus, S. agalactiae, and E. coli were in the range of 0.78-6.25 μL/mL. The time-kill tests indicated that the essential oils' antibacterial activity depended on concentration and contact time. All three essential oil-based post-milking teat spray preparations showed good stability. The citronella spray formulation showed the highest antibacterial potency. In in vivo testing, the citronella spray eradicated aerobic bacteria on the teat skin of cows (99.9% or 3-log10 reduction) within 1 min, which was non-inferior to a standard 0.54% iodine solution teat dip. Clove, citronella, and sweet basil essential oils were effective against S. aureus, S. agalactiae, and E. coli in vitro. Of these, citronella essential oil is the most promising to be developed as a post-milking teat spray with high antibacterial activity and excellent bacterial eradication properties in vivo.