• Joon Young Song, Sae Yoon Kee, In Sook Hwang, Yu Bin Seo, Hye Won Jeong, Woo Joo Kim, and Hee Jin Cheong.
• Division of Infectious Diseases, Department of Internal Medicine, College of Medicine, Korea University, Seoul, Republic of Korea.
• J. Antimicrob. Chemother. 2007 Aug 1;60(2):317-22.

ObjectivesTo determine the in vitro activities and interactions of imipenem, colistin and tigecycline with old antibacterial agents against carbapenem-resistant Acinetobacter baumannii.MethodsForty-three carbapenem-resistant A. baumannii isolates from the intensive care unit of a university hospital were collected and their MICs of imipenem, colistin and tigecycline were determined. With eight randomly selected carbapenem-resistant isolates, an in vitro time-kill study was performed for the evaluation of antibacterial activity of colistin, tigecycline, imipenem/sulbactam and colistin/rifampicin.ResultsThe time-kill study of colistin demonstrated bactericidal activity against A. baumannii at concentrations of 4xMIC and 8xMIC, whereas tigecycline showed bacteriostatic activity at all concentrations. The combination regimens of imipenem/sulbactam and colistin/rifampicin were synergistic and bactericidal at 1xMIC.ConclusionsImipenem/sulbactam combination, colistin and tigecycline showed good in vitro activities against carbapenem-resistant A. baumannii isolates. Even though colistin is bactericidal against carbapenem-resistant A. baumannii, the colistin/rifampicin combination is more warranted in order to be certain.

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