Abstract: Corynebacterium pseudotuberculosis (Cp) infection highly impairs the production performance of livestocks, especially for the small ruminants (sheep/goats). This experiment was conducted to screen the essential oils against Cp, and to evaluate its antibacterial mechanism. Bergamot essential oil (BEO) was screened from four kinds of essential oils by K-B disk diffusion method, and the minimal inhibitory concentration (MIC) of BEO against different strains of Cp was determined by resazurin based broth dilution method. The effect of BEO on Cp infection of J774A. 1 macrophages were detected through in vitro experiments. The bacterial load in visceral organs, antimicrobial peptide genes expression in spleens and survival rates were tested to evaluate the protective effects of BEO on Cp-infected Kunming mice in vivo. Then the antibacterial mechanism of BEO was explored via the changes of cell morphology, cellular nucleotide leakage and the expression of virulence genes of Cp. The MIC value of BEO against Cp is 0.78-1.56 μL·mL^-1. The treatment of BEO significantly reduced the bacterial loads in kidney, liver and ascites of Cp-infected mice (P<0.01), up-regulated the mRNA expression levels of antibacterial peptides genes including Cramp, Bpifal 1, mBD2, mBD3 and mBD4 in spleens (P<0.01), decreased infection rate of Cp in J774A.1 macrophages and reduced mortality of Cp-infected mice (P<0.05). Scanning electron microscope analysis showed that the cell membrane was destroyed, the nucleotide was significantly leaked in Cp treated with BEO, and the mRNA expression level of virulence gene phospholipase D (pld) was significantly decreased in BEO treated Cp (P<0.01). BEO possesses strong antibacterial activity against Cp, and alleviates the infectious degree of Cp in mice, the mechanism of which may be related to the disruption of membrane integrity and inhibition of pld mRNA expression of Cp treated with BEO.

Key words: essential oil, Corynebacterium pseudotuberculosis, antibacterial activity, mechanism