Phenotypic and molecular characterization of carbapenem-resistant Acinetobacter baumannii isolates from ventilator associated pneumonia patients

Background: Multi- drug resistant Acinetobacter baumannii (A. baumannii) is considered a major cause of ventilator associated pneumonia (VAP) among intensive care unit (ICU) admitted patients. The objectives of this study were to determine the prevalence of carbapenem - resistant A. baumannii causing VAP in ICU and to investigate the presence of carbapenem hydrolyzing class D b-lactamase genes among the studied isolates. Methods: In a cross-sectional study, A. baumannii was isolated from VAP patients and its antibiotic susceptibility was detected. Carbapenem resistance was determined phenotypically by modified carbapenem inactivation method (mCIM) and genotypically by polymerase chain reactions for detection of class D b-lactamases including; blaOXA-51-like gene, blaOXA-23-like, blaOXA-24-like, and blaOXA-58- like genes. Results: Forty-six A. baumanii were isolated from 140 respiratory specimens collected from VAP patients. Using disc diffusion methods, all A. baumanii isolates were multidrug resistant (100%) and 39 (84.7%) of them were carbapenem resistant. Carbapenemases genes were positive in 36 (92.3%) of carbapenem resistant A. baumanii. Using mCIM test, carbapenemases were detected in 34 (87.2%) carbapenem resistant A. baumanii. Non-significant agreement existed between phenotypic and genotypic detection methods of carbapenemases (Kappa= 0.1 and p value 0.4). Conclusion: Carbapenem-resistant A. baumannii isolates were responsible for a significant number of VAP in intensive care unit admitted patients. Carbapenemases genes especially OXA 23 were frequent in A. baumannii.