Molecular mechanisms of antibiotic co-resistance among carbapenem resistant Acinetobacter baumannii

The spread of carbapenem-resistant Acinetobacter baumannii (CRAB) is difficult to control especially in the hospitals due to the successful mobilization and evolution of the genetic elements harboring the resistant determinants. The study was conducted to examine the distribution of aminoglycosides, tetracycline, and sulfonamide-resistant determinants among CRAB isolates that carry the blaOXA-23 gene. For a total of 160 CRAB strains isolated at tertiary care hospitals of Pakistan that mainly carried blaOXA-23 gene were included in the study to evaluate the assortment of antibiotic resistance genes. The susceptibility rates of CRAB for other than beta-lactam drugs were 2.5% for both ciprofloxacin and aminoglycosides and 18% and 25% for sulfonamides and tetracyclines, respectively. Polymyxin B (MIC90, 1 g/mL) Colistin (MIC90, 1 g/mL) and Tigecycline (MIC90, 2 g/mL) were most active against these extensively drug-resistant CRAB isolates. The isolates were found to possess various genes mainly the tetB and sul2 for tetracycline and sulfonamide but the genes conferring resistance to aminoglycosides were varied with various combinations. Despite the CRAB clones containing blaOXA-23 have been previously reported in Pakistani hospitals, the screening of genetic determinants responsible for other antimicrobial agents is crucial for developing an effective surveillance and mitigation system for infection management.