Selective antibacterial activity of Citrus Medica limonum essential oil against Escherichia coli K99 and Lactobacillus acidophilus and its antibacterial mechanism

Abstract

Escherichia coli K99 (E. coli K99) is one of the important pathogenic bacteria in calf production causing massive loss every year, and Lactobacillus acidophilus (L. acidophilus) is an important probiotic in the gut. Essential oils in Citrus have selective antibacterial activity and the capacity to be an alternative to antibiotics. In this study, we analyzed the chemical component of Citrus Medica Limonum essential oil (LEO) and d-limonene, β-pinene, and γ-terpinene by GC-MS, then compared their selective antibacterial activities against E. coli K99 and L. acidophilus and investigated the antibacterial mechanism of LEO. The principal component of LEO, d-limonene, β-pinene, and γ-terpinene were d-limonene (47.19%), d-limonene (77.94%), β-pinene (93.52%) and γ-terpinene (89.27%) respectively. The MIC and MBC of LEO against E. coli K99 were 5 mg/mL and 10 mg/mL, while against L. acidophilus were 80 mg/mL and 160 mg/mL, which showed its best selective antibacterial activity among four EOs. LEO damaged the cell membrane structure, leading to the leakage of intracellular proteins and nucleic acids of both bacteria. Moreover, LEO improved the cell-surface hydrophobicity of both bacteria and decreased the soluble protein content of E. coli K99. In conclusion, LEO has selective antibacterial activity and the potential to be applied in calf feed.