Colistin, doxycycline and Labetalol-meropenem combination are the most active against XDR-Carbapenem-resistant Acinetobacter baumannii: Role of a novel transferrable plasmid conferring carbapenem resistance.

This study aimed to evaluate the antimicrobial susceptibility and combination of a beta-blocker, labetalol (LAB) and meropenem (MEM) on Carbapenem-resistant (CR) A. baumannii clinical isolates. A total of 43 CR- A. baumannii were isolated of which 37 (86.6 %) and 28 (65 %) exhibited MDR and XDR phenotypes, respectively. Colistin and doxycycline still retain their activities in 93.1 % and 72.1 % of the isolates, respectively. Combining MEM with LAB at 0.25 mg /mL, decreased MIC values in 91.4 % (32/35) however, at 0.5 mg /mL, it decreased MIC value and restored susceptibility to MEM in 100 % and 91.4 % of the tested isolates, respectively. A novel transferable plasmid pAcbGIM3 harboring aph-3', blaoxa-58,blaGIM3 and blaCTX-M3 and eight mobile genetic elements were successfully isolated from a pan-drug resistant (PDR) isolate. In conclusion, LAB-MEM is a promising combination and should be clinically examined. This is the first report of a transmissible plasmid harboring blaGIM3 gene in Egypt.