Abstract: [Objective] To reduce the use of veterinary antibiotics,explore the in vitro synergistic antibacterial effect of the combination of traditional Chinese medicine compound and cephalosporin antibiotics on multi-drug resistant Staphylococcus aureus （MRSA） in dairy cows with mastitis,and screen combined medication regimens that enhance efficacy and reduce toxicity. [Method] In this study,MRSA strains were isolated and identified from the breast secretions of clinically affected dairy cows. The minimum inhibitory concentrations （MIC） of a traditional Chinese medicine compound （consisting of six traditional Chinese medicines such as dandelion,honeysuckle,and forsythia） and two cephalosporin antibiotics,ceftiofur and cefquinome,were determined by the micro-broth dilution method. The synergistic antibacterial index （FICI） of the combined medication was detected by the checkerboard dilution method,and the effects of different drug combinations on the MRSA growth curve were observed. [Result] The individual MIC of the isolated MRSA strains for ceftiofur and cefquinome were 64,32μg/mL respectively,and the individual MIC of the traditional Chinese medicine compound was 256 mg/mL. The FICI of the combination of the traditional Chinese medicine compound with ceftiofur and cefquinome was 0.38 and 0.25 respectively,both showing significant synergistic antibacterial effects. The inhibitory effect of the combined medication group on the growth of MRSA was stronger than that of the single medication group,which could shorten the onset time of the antibacterial effect and prolong the duration of the antibacterial effect. [Conclusion] The combination of traditional Chinese medicine compound and cephalosporin antibiotics can significantly reduce the inhibitory concentration of the latter against MRSA,enhance the inhibitory effect,and decrease the clinical dosage of cephalosporin antibiotics. This provides a new medication idea and experimental basis for the treatment of drug-resistant strain infections in dairy cow mastitis.

Key words: Chinese herbal compound, cephalosporin antibiotics, dairy cow mastitis, multidrug-resistant Staphylococcus aureus, synergistic bacteriostatic effect