Carbapenem-resistant Acinetobacter baumannii and Pseudomonas aeruginosa: characterization of carbapenemase genes and E-test evaluation of colistin-based combinations.

Abstract

BackgroundCarbapenamase producing Acinetobacter baumannii and Pseudomonas aeruginosa are emerging worldwide limiting the use of carbapenems as effective and safe drugs.PurposeTo characterize different carbapenemase genes carried by carbapenem-resistant (CR) A. baumannii and P. aeruginosa isolates and to evaluate the in vitro effect of some colistin-based combinations by E-test method in Zagazig University Hospitals ICU isolates.MethodsCR A. baumannii and P. aeruginosa isolated from the surgical intensive care unit (ICU) were tested for carbapenemase genes by polymerase chain reaction and the effect of colistin/meropenem and colistin/tigecycline combinations was evaluated by E-test.ResultsGenes coding for OXA-23, NDM and GES were detected in 90, 66.7 and 50% of CR A. baumannii, respectively, while genes coding for VIM, GES, NDM and IMP were detected in 50, 40.9, 27.3 and 18.2% of CR P. aeruginosa, respectively. Colistin/tigecycline combination showed synergistic and additive effect in 20% and 60% of A. baumannii isolates, respectively, while colistin/meropenem combination showed synergistic and additive effect in 63.6% and 36.4% of P. aeruginosa, respectively.ConclusionCarbapenemase genes carriage accounts for high level carbapenem resistance in our isolates. Colistin/tigecycline and colistin/meropenem combinations can be considered for treatment of severe infections by CR A. baumannii and P. aeruginosa, respectively.