The efficacy of colistin monotherapy versus combination therapy with other antimicrobials against carbapenem-resistant Acinetobacter baumannii ST2 isolates.

This study aimed to investigate the efficacy of colistin both alone and in combination with either meropenem or levofloxacin against CRAB clinical isolates. The OXA carbapenemase genes and multilocus sequence typing were detected after 35 CRAB isolates biochemical identification. Then, the minimum inhibitory concentrations, minimum bactericidal concentrations, antibiotic interactions of the test antibiotics, and synergistic effects were determined by the checkerboard method and time-kill assays. The chromosomal gene bla OXA-51-like was detected in all isolates, and bla OXA-23-like and bla OXA-24-like were present in 91.4% and 25.7% of the isolates, respectively. The combination of colistin and meropenem displayed the highest rate of synergy (51.4%) against the 35 isolates, while the colistin-levofloxacin combination showed a higher rate of indifference interaction (22.9%) than that of the colistin-meropenem (8.6%) combination. The synergistic effect of colistin against the CRAB isolates was confirmed. The combination of colistin with meropenem is recommended against CRAB isolates.