Genetic characterization and in vitro activity of antimicrobial combinations of multidrug-resistant Acinetobacter baumannii from a general hospital in China

The present study aimed to develop a rational therapy based on the genetic epidemiology, molecular mechanism evaluation and antibiotic combinations activity in multidrug-resistant (MDRAB). MDRAB was screened by the Kirby-Bauer method. The random amplified polymorphic DNA technique was used to establish genetic fingerprinting, and a series of resistance genes were detected by polymerase chain reaction. Antimicrobial agents including amikacin (AK), cefoperazone/sulbactam (SCF I/II), meropenem (MEM), minocycline (MINO) and ciprofloxacin (CIP) were used to determine the minimum inhibitory concentrations (MICs) and interactions between antibiotics by the broth microdilution method and chequerboard assays. In total, 34 MDRAB strains were isolated and classified into 8 phenotypes A-H, according to their general drug susceptibilities. A total of 4 major genotypes (I-IV) were clustered at 60% a genotypic similarity threshold. High positive rates of β-lactamase , topoisomerase IV, oxacillinase ( )-23, AdeB family multidrug efflux RND transporter , β-lactamase , class 1 integrons ( ), 16S rRNA methylase , phosphotransferase (3), 16S rRNA methyltransferase were presented to exceed 90%, acetylyltransferase , , , 16S rRNA methylase , oxacillinase and metallo-β-lactamase genes demonstrated positive rates of 29.4-85.29%, while two-component system was not observed in any strain. MEM+SCF I or SCF II primarily exhibited synergistic effects. AK+SCF I, AK+SCF II, MINO+SCF I, MINO+SCF II, MINO+CIP and MINO+MEM primarily presented additive effects. AK+CIP demonstrated 70.59% antagonism. The antibacterial activity of SCF I was superior compared with that of SCF II. The results indicated the polyclonal genetic epidemiological trend of MDRAB in the Second Xiangya Hospital, and verified the complexity of genetic resistance. In addition, combinations suggested to be efficacious were MEM+SCF I and MEM+SCF II, which were more effective compared with other combinations for the management of MDRAB infection.