To explore the effect of Bufonis Venenum ethanol extract on the sensitivity of multidrug-resistant Pseudomonas aeruginosa(MDRPA) to ceftazidime through the MexAB-OprM efflux pump system.Methods:P.aeruginosa strains positive for the MexAB-OprM system were screened.An in vitro antibacterial model for MDRPA was established using the broth dilution method,and the minimum inhibitory concentration(MIC) of the Bufonis Venenum ethanol extract and its combination with ceftazidime was determined.The mRNA expression levels of mexB,mexR,and oprM genes in the MexAB-OprM efflux pump system were detected by real-time fluorescence reverse transcription PCR before and after intervention with the Bufonis Venenum ethanol extract.Results:The MIC value of the Bufonis Venenum ethanol extract against MDRPA was 6.25 mg/mL.The combination index of Bufonis Venenum ethanol extract with ceftazidime was less than 1,indicating a synergistic effect between the two drugs.As the concentration of the Bufonis Venenum ethanol extract increased,the relative expression levels of mexB and oprM in the MexAB-OprM efflux pump decreased(P<0.05),while the relative expression of mexR increased(P<0.05).Conclusion:The Bufonis Venenum ethanol extract enhances the sensitivity of MDRPA to ceftazidime by inhibiting the expression of the MexAB-OprM efflux pump.