In Vitro Activity of Imipenem and Colistin against a Carbapenem-ResistantKlebsiella pneumoniaeIsolate Coproducing SHV-31, CMY-2, and DHA-1

摘要

We investigated the synergism of colistin and imipenem against a multidrug-resistantK. pneumoniaeisolate which was recovered from a severe hip infection. PCR and DNA sequencing were used to characterize the outer membrane porin genes and the resistance genes mediating the commonβ-lactamases and carbapenemases. Synergism was evaluated by time-kill studies. TheblaSHV-31,blaCMY-2, andblaDHA-1were detected. Outer membrane porin genes analysis revealed loss ofompK36and frame-shift mutation ofompK35. The common carbapenemase genes were not found. Time-kill studies demonstrated that a combination of 1x MIC of colistin (2 mg/L) and 1x MIC of imipenem (8 mg/L) was synergistic and bactericidal but with inoculum effect. Bactericidal activity without inoculum effect was observed by concentration of 2x MIC of colistin alone or plus 2x MIC of imipenem. In conclusion, colistin plus imipenem could be an alternative option to treat carbapenem-resistantK. pneumoniaeinfections.