Expression of metallo-β-lactamase genes in carbapenem resistant Acinetobacter baumannii isolates from intensive care unit patients

Abstract

Background: Acinetobacter baumannii (A. baumannii) is Gram-negative, aerobic coccobacillus. It causes life-threatening nosocomial infections, particularly in immunocompromised patients. Carbapenem-resistant A. baumannii are prevalent worldwide mostly caused by carbapenemase synthesis. Metallo β-lactamases (MBLs) include imipenemase (IMP), New Delhi metallo-β-lactamases (NDM) and Verona integrin metallo-β-lactamase (VIM). We aimed to investigate the prevalence of MBLs genes expression in carbapenem-resistant A. baumannii isolated from ICU patients as a reliable method for reducing the morbidity & mortality of these patients.

Methods: Using conventional methods, 87 A. baumannii isolates were identified from 103 ICU patient specimens. Metallo β-lactamases were detected phenotypically in imipenem-resistant strains using a combined disc test (CDT). Real-time PCR was used to quantitate the expression of the blaIPM, blaNDM & blaVIM genes.

Results: Imipenem resistance was identified in 82.8% of patients. Combined disc test was positive in 44.4% of imipenem-resistant isolates. For metallo-lactamases gene expression, blaVIM had a higher median value than blaNDM and blaIPM (0.5, 0.1 and 0 respectively). Combined disc test was found to have a statistically significant relationship with both NDM and VIM gene expression, which was considerably higher in isolates with positive CDT. Both NDM and VIM gene expression had a statistically non-significant correlation with CDT value, but their expression had a statistically significant negative correlation with CD zone of inhibition value.

Conclusion: The expression of blaVIM and blaNDM genes is directly correlated with the level of MBLs production and the level of these enzymes can be detected phenotypically depending on its negative correlation with the CD zone of inhibition diameter.