ObjectiveTo establish an extensively drugresistant Acinetobacter baumannii(XDRAB) infection model using Caenorhabditis elegans(C. elegans), and evaluate the effect of efflux pump inhibitors(EPIs) on reversal of ciprofloxacin resistance in XDRAB. MethodsXDRAB infection model of C. elegans was established, six EPIs(CCCP, PAβN, NMP, omeprazole, reserpine, and verapamil）combined with ciprofloxacin were used to treat the infected model, the survival rate of C. elegans was recorded to evaluate the in vivo activities of drugs, toxicity test and in vitro drug susceptibility test were also performed.ResultsLethal effect of different concentrations of XDRAB on C. elegans was varied, 5×106 CFU/mL of XDRAB was selected to infect C. elegans. C. elegans survival test showed that survival curves of C. elegans infected with XDRAB for 3 hours and curves of control group (polymixin B was added) were not significantly different （χ2=3.154，P＞0.05）; compared with control group, survival curves of C. elegans infected with XDRAB for 6 hours or 9 hours were significantly different (both P<0.001), but 6 hours and 9 hours were not significantly different（χ2=0.669，P＞0.05），6 hours was chosen as the duration of infection, 36 hours was appropriate for the duration of antimicrobial therapy. Ciprofloxacin with EPIs for infection model revealed that low concentration of PAβN, NMP, omeprazole, and reserpine could improve the survival rate of C. elegans by 30%-40%, 15%-20%, 20%-30%, and 20% respectively, high concentration of verapamil could improve the survival rate of infected C. elegans by about 30%. In vitro susceptibility test and toxicity test results showed that ciprofloxacin combined respectively with CCCP, omeprazole, and verapamil could reduce minimum inhibitory concentration(MIC) to the original 1/4, combined respectively with PAβN，NMP, and reserpine could reduce MIC to the original 1/2, CCCP had the best bacterial inhibitory effect in vitro, but the toxicity was large, and was not suitable for the study of pharmacodynamics in vivo. ConclusionThe infection model of C. elegansXDRAB is initially and successfully established, which is used to evaluate the efficiency of six EPIs for reversing ciprofloxacin resistance.