Evaluation of the Relative Frequency of Carbapenemase Genes by Phenotypic and Genotypic Methods in Pseudomonas aeruginosa Isolates from Patients with Open Heart Surgery in Iran

Backgrounds: Carbapenem resistance among Pseudomonas aeruginosa strains is alarming. This study aimed to investigate the relative frequency of carbapenem-resistant P. aeruginosa strains by phenotypic and genotypic methods. Materials & Methods: The antibiotic susceptibility pattern of ۶۰ P. aeruginosa isolates was determined by disk diffusion method (Kirby-Bauer). BD Phoenix automated microbiology system was used to identify carbapenem-resistant isolates, and the minimum inhibitory concentration (MIC) was determined using E-Test. In addition, mCIM (modified carbapenem inactivation method) phenotypic test was performed to evaluate carbapenem resistance genes in P. aeruginosa isolates. The prevalence of metallo-beta-lactamase (MβL) genes in carbapenem-resistant P. aeruginosa isolates was determined using conventional polymerase chain reaction (PCR). Findings: The frequency of carbapenem-resistant P. aeruginosa isolates was ۳۶% (۲۲ of ۶۰). The highest resistance was observed to imipenem and meropenem (۳۶.۶%), and the highest sensitivity was observed to amikacin (۷۵%). All carbapenem-resistant P. aeruginosa isolates were confirmed by the BD Phoenix automated system (MIC> ۸ µg/mL for imipenem and meropenem), E-test (MIC ˂۳۲ µg/mL), and mCIM assay (the growth inhibition zone diameter was ۶-۸ mm).  In carbapenem-resistant P. aeruginosa isolates, the frequency of blaVIM, blaIMP, and blaSPM genes was ۹.۱% (۲ of ۲۲), ۴.۵% (۱ of ۲۲), and ۴.۵% (۱ of ۲۲), respectively. BlaKPC and blaNDM genes were not found in any of the isolates. Conclusion: Based on the present study results, all phenotypic tests used to identify carbapenemase-producing isolates had the same sensitivity (۱۰۰%) and specificity (۱۰۰%).

Keywords:

Carbapenemases , Pseudomonas aeruginosa , Phenotypic , Bacterial sensitivity tests