Comparison of Phenotypic Tests-Carba NP and  Modified Carba NP Test for Rapid Detection of  Carbapenem Resistance in Escherichia coli

Ravi Vashistha; Siva Prasad Reddy B; Sapna Chauhan

Ravi Vashistha PhD Scholar, Department of Microbiology, NIMS University, Jaipur, Rajasthan, India
Siva Prasad Reddy B Professor, Department of Microbiology, NIMS University, Jaipur, Rajasthan, India
Sapna Chauhan Professor and HOD, Department of Microbiology MMC, Muzaffarnagar, Uttar Pradesh, India

Keywords: Carba NP, carbapenem resistance, Modified Carba NP

Abstract

Background: To determine the antibiotic resistance pattern, the prevalence of extended-spectrum beta-lactamases (ESBLs) and carbapenem resistance in blood culture isolates of E. coli. Further, we evaluated and compared Carba NP, Modified Carba NP
Methods: Initial screening was performed, following which 21 carbapenem-resistant strains and four carbapenem-susceptible strains were selected for further analysis. Two phenotypic methods—the Carba NP test and the Modified Carba NP test—were evaluated according to Clinical Laboratory Standards Institute
(CLSI) guidelines. These assays rely on the biochemical detection of carbapenem hydrolysis, specifically the breakdown of the imipenem beta-lactam ring, which induces a colour change in a pH indicator.
Results: The Carba NP test yielded positive results in 18 of the 21 resistant isolates, while the Modified Carba NP test was positive in 20 out of 21 isolates.
Conclusion: The Modified Carba NP test is easier and cheaper than the Carba NP test, making it possible to find carbapenemase activity directly from Escherichia coli bacterial cultures. The test could be used in low-income countries with large reservoirs for carbapenemase producers and can be implemented in any laboratory
worldwide.

How to cite this article:
Vashistha R, Reddy B S P, Chauhan S. Comparison of Phenotypic Tests-Carba NP and Modified Carba NP Test for Rapid Detection of Carbapenem Resistance in Escherichia coli. J Commun Dis. 2025;57(2):32-36.

DOI: https://doi.org/10.24321/0019.5138.202534

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