Evaluation of Carba NP Version II Test for Rapid Detection and Categorization of Carbapenemases Produced by Klebsiella Pneumoniae Clinical Isolates

Abstract

Background: Carbapenemase producing K. pneumoniae poses severe clinical problems. The accurate phenotypic detection and differentiation of the carbapenemase types in clinical laboratories is now of utmost importance for the determination of appropriate therapeutic schemes and the implementation of infection control measures. Objective: to identify the prevalent carbapenemases among carbapenem non-susceptible K. pneumoniae isolated from AMUH, to evaluate the ability of Carba NP version II test to detect carbapenemase production and identify their Ambler classes compared to PCR as a gold standard, in addition to comparing the Carba NP version II test with MHT and inhibitor-based phenotypic tests regarding sensitivity, specificity, turnaround time and cost effectiveness. Methodology: This study was carried out on 96 non-duplicate carbapenem non-susceptible K. pneumoniae isolates carrying one or more of carbapenemase genes. phenotypic screening methods included: Carba NP II test, MHT, meropenem/PBA CDT and meropenem/EDTA CDT. Results: Carbapenemase class B was the most prevalent (94.8%). Carba NP II showed the highest sensitivity in detecting class B (72.5%) with PPV (95.7%). Increase in the number of class B genes in a given isolate, improved the sensitivity from 55.6% to 80%. The Carba NP II test was found to be 15% sensitive and 91.7% specific in detecting class D and it could not detect class A in any of the 19 isolates that harbored KPC gene. Conclusion: The main advantages of Carba NP II test over CDT and MHT are; the rapidity of the test and its relatively higher sensitivity in detecting class B carbapenemases.