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

Background: Carbapenamase producing and are emerging worldwide limiting the use of carbapenems as effective and safe drugs.

Purpose: To characterize different carbapenemase genes carried by carbapenem-resistant (CR) and isolates and to evaluate the in vitro effect of some colistin-based combinations by E-test method in Zagazig University Hospitals ICU isolates.

Methods: CR and 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.

Results: Genes coding for OXA-23, NDM and GES were detected in 90, 66.7 and 50% of CR , respectively, while genes coding for VIM, GES, NDM and IMP were detected in 50, 40.9, 27.3 and 18.2% of CR , respectively. Colistin/tigecycline combination showed synergistic and additive effect in 20% and 60% of isolates, respectively, while colistin/meropenem combination showed synergistic and additive effect in 63.6% and 36.4% of , respectively.

Conclusion: Carbapenemase 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 and , respectively.