Objective:To investigate the Acinetobacter baumannii’s distribution feature、the antimicrobial resistance of Acinetobacter baumannii isolated during the past 4 years and compare antibacterial activity of Polymyxin B against multidrug-resisitant(MDR) Acinetobacter baumannii with that of Imipenem in vitro.Methods:The distribution feature of infection caused by Acinetobacter baumannii was supervised.Disk diffusion test was used to study the antimicrobial agents resistance of Acinetobacter baumannii and transition of drug resistance.The results were evaluated based on Clinical and Laboratory Standards Institute(CLSI).The MDR Acinetobacter baumannii were screened by WHONET 5.MICs(minimal inhibitory concentration)of Polymyxin B and imipenem were detected by broth dilution method.Results:Constituent ratio of infections caused by Acinetobacter baumannii had been incresed in the recent 4 years

especially in intensive care unit.Although carbapenems were the most active antibiotics tested against Acinetobacter baumannii

the resistance rate had been sharply raised since 2008.In addition

the ratio of MDR Acinetobacter baumannii had also been raised in the 4 years.The results of MIC displayed that Polymyxin B had the higher antibacterial activity against the MDR Acinetobacter baumannii than Imipenem. Conclusion:Proportion of nosocomial infection caused by Acinetobacter baumannii significantly increased.The resistance rate of Acinetobacter baumannii had been rised obviously and the number of MDR Acinetobaeter baumannii had been increased sharply. Monitoring of the antimicrobial agents resistance to Acinetobacter baumannii should be strengthened.Polymyxin B still shows strong antibacterial activity on the MDR Acinetobacter baumannii in vitro.We can consider using Polymyxin B to treat the severe infections caused by MDR Acinetobacter baumannii.