Genetic Characterization of Carbapenem Resistant Acinetobacter baumannii in Tertiary care settings of Lahore, Pakistan

Saadia Ijaz, Farheen Ansari, Muhammad Nawaz, Aftab Ahmad Anjum, Karam Rasool


Background: Acinetobacter baumannii is major cause of ventilator associated pneumoniae (VAP) as it is an opportunistic nosocomial organism. The current study was to find out the antibiotic resistance pattern of Acinetobacter baumannii, its phenotype and the genetic characterization of Metallo-β-Lactamase (MBL) genes that are responsible for carbapenem resistance.

Methods: One hundred and fifty Carbapenem resistant Acinetobacter baumannii (CRAB) specimens were isolated and PCR amplification of organism specific bla-OXA-51gene was performed and antibiotic susceptibility was checked. Phenotypic susceptibility analysis was performed by Modified Hodge Test (MHT) and Imipenem-EDTA Double Disc Synergy Test (IMP-EDTA DDST). The carbapenemases and MBL producing genes were amplified by PCR.

Results: CRAB showed high resistance against piperacillin/tazobactam (99.3%), cefepime and ceftazidime (99.3% each), amikacin (91.3%), ciprofloxacin (96.7%) and levofloxacin (96.7%). Only one isolate showed resistance to colistin. The isolates positive for both MHT and DDST (n=70) were further characterized to detect metallo-β-lactamase genes. Molecular characterization revealed the presence of bla-OXA-51 gene in all tested isolates (100%) followed by bla-VIM 89%, bla-OXA-23 64%, respectively and so on. Few genes coexisted with each other including bla VIM, bla OXA 23, bla OXA 51 and bla NDM-1.  None of the isolate was found positive for bla-IMP gene.

Conclusion: It is concluded that CRAB isolates exhibited a high rate of resistance towards antimicrobials because of the presence of drug hydrolyzing enzymes, carbapenemases and MBLs. This is among the rare study reported recently indicating CRAB isolates co-harboring many resistant genes are very difficult to treat. There is a dire need to develop novel antibiotics against resistant A. baumannii to minimize its prevalence. Moreover, it is recommended that colistin treatment in the clinical settings should be continuously monitored in order to prevent the development of resistance.

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