The carbapenem inactivation method (CIM), a simple and low-cost alternative for the Carba NP test to assess phenotypic carbapenemase activity in gram-negative rods.

Kim Van Der Zwaluw,Hester J Bootsma,Gerlinde N Pluister,Angela De Haan,Leo M Schouls,Albert J De Neeling,Holger Rohde

doi:10.1371/journal.pone.0123690

Kim Van Der Zwaluw, Hester J Bootsma + Show 5 more

Open Access

https://doi.org/10.1371/journal.pone.0123690

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Abstract

A new phenotypic test, called the Carbapenem Inactivation Method (CIM), was developed to detect carbapenemase activity in Gram-negative rods within eight hours. This method showed high concordance with results obtained by PCR to detect genes coding for the carbapenemases KPC, NDM, OXA-48, VIM, IMP and OXA-23. It allows reliable detection of carbapenemase activity encoded by various genes in species of Enterobacteriaceae (e.g., Klebsiella pneumoniae, Escherichia coli and Enterobacter cloacae), but also in non-fermenters Pseudomonas aeruginosa and Acinetobacter baumannii. The CIM was shown to be a cost-effective and highly robust phenotypic screening method that can reliably detect carbapenemase activity.

Highlights

The emergence and spread of carbapenemase-producing Gram-negative rods is a worldwide emerging public health threat [1,2,3]
The Carbapenem Inactivation Method (CIM) is the first to use antibiotic susceptibility-testing disks, which are globally available at low cost and have long shelf lives, as substrate aliquots for this
The application of the CIM in this study shows that it is capable of detecting carbapenemase production in Gram-negatives allowing distinction between carbapenem-resistance due to beta-lactamase activity and reduced permeability

Summary

Introduction

The emergence and spread of carbapenemase-producing Gram-negative rods is a worldwide emerging public health threat [1,2,3]. In health care centers, this may pose a major problem as carbapenems are becoming more frequently needed to treat infections caused by Gram-negative bacteria that produce extended spectrum beta-lactamases (ESBL) [4,5]. High or low minimal inhibitory concentrations (MICs) do not necessarily reflect the production of carbapenemases, as other mechanisms such as porin loss or increased efflux pump activity, due to alterations in chromosomally located genes, can cause resistance [7,8]. Since carbapenemase-encoding genes are often located on plasmids, this type of resistance is much more likely to spread [9]

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