Abstract: The misuse of antibiotics on farms has caused the emergence of a variety of drug-resistant bacteria. MRSA isolated from dairy meat products are increasing year by year, leading to a great threat to food safety in the farming industry. In this paper, berberine hydrochloride (BBR), a natural product with combined inhibition effect of MRSA with levofloxacin, was screened, and the synergistic inhibition effect and combined inhibition mechanism of BBR with its effect on MRSA were investigated. The results showed that BBR could effectively inhibit the growth of MRSA and improve the sensitivity of MRSA to levofloxacin, and the combination could reduce the MIC of the latter up to 1/16. The synergistic mechanism of combination was mainly up-regulation of ribA and down-regulation of mec A and msc L expression levels, disrupting the cell wall and increasing the permeability of the cell membrane, thus achieving synergistic bacterial inhibition. This thesis helps to lay the foundation for reducing the use of antibiotics in livestock farming and improving the food safety of meat and milk.

Key words: natural products, antibiotics, bacteriostatic MIC, co-inhibition, mechanism of bacterial inhibition