Evaluation of direct Carba-NP (CNPt) for screening of carbaenemases production in Gram negative bacilli

Document Type : Original Article


Medical Microbiology and Immunology Department, Faculty of medicine, Ain Shams University, Egypt


Background: Carbapenem resistance among gram negative bacilli (GNB) is a major threat to human health. Rapid and accurate detection of carbapenemase production is very important for clinical management, epidemiological purposes and infection prevention and control issues. Direct Carba NP test (CNPt) is a modified CNPt that allows rapid detection of carbapenemases at a lower cost and improved sensitivity. This work aimed to evaluate direct-CNPt for detection of cabapenemases production as a screening and confirmatory test in GNB versus multiplex PCR as the gold standard test. Methods: This study was conducted on 50 clinical isolates of GNB derived from different clinical samples according to their resistance to meropenem (zone of inhibition ≤ 23 mm). Direct CNPt was performed on all 50 clinical isolates using bacterial colonies directly. A change in colour was observed after (̰ 2 h). A multiplex PCR was performed on all isolates to detect bla KPC, bla IMP, bla VIM and bla NDM, and bla OXA-48 genes. Results: The overall sensitivity and specificity of direct CNPt as compared to multiplex PCR were 95.2% and 100% respectively. The sensitivity to OXA-48 and IMP genes were relatively lower (91.6 % and 85.7 % respectively) than other genes which had 100% sensitivity for each. Conclusion: Direct CNPt is a reliable and rapid method that allows detection of different carbapenemases at a reduced cost. It could be used in combination with other phenotypic or genotypic assays in settings where OXA-48 and IMP are of high prevalence.


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