Modified carbapenem inactivation method for phenotypic detection of carbapenemase production among enterobacteriaceae

Virginia M. Pierce, Patricia J. Simner, David R. Lonsway, Darcie E. Roe-Carpenter, J. Kristie Johnson, William B. Brasso, April M. Bobenchik, Zabrina C. Lockett, Angella Charnot-Katsikas, Mary Jane Ferraro, Richard B. Thomson, Stephen G. Jenkins, Brandi M. Limbago, Sanchita Das

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163 Scopus citations

Abstract

The ability of clinical microbiology laboratories to reliably detect carbapenemase-producing carbapenem-resistant Enterobacteriaceae (CP-CRE) is an important element of the effort to prevent and contain the spread of these pathogens and an integral part of antimicrobial stewardship. All existing methods have limitations. A new, straightforward, inexpensive, and specific phenotypic method for the detection of carbapenemase production, the carbapenem inactivation method (CIM), was recently described. Here we describe a two-stage evaluation of a modified carbapenem inactivation method (mCIM), in which tryptic soy broth was substituted for water during the inactivation step and the length of this incubation was extended. A validation study was performed in a single clinical laboratory to determine the accuracy of the mCIM, followed by a nine-laboratory study to verify the reproducibility of these results and define the zone size cutoff that best discriminated between CP-CRE and members of the family Enterobacteriaceae that do not produce carbapenemases. Bacterial isolates previously characterized through whole-genome sequencing or targeted PCR as to the presence or absence of carbapenemase genes were tested for carbapenemase production using the mCIM; isolates with Ambler class A, B, and D carbapenemases, non-CP-CRE isolates, and carbapenem-susceptible isolates were included. The sensitivity of the mCIM observed in the validation study was 99% (95% confidence interval [95% CI], 93% to 100%), and the specificity was 100% (95% CI, 82% to 100%). In the second stage of the study, the range of sensitivities observed across nine laboratories was 93% to 100%, with a mean of 97%; the range of specificities was 97% to 100%, with a mean of 99%. The mCIM was easy to perform and interpret for Enterobacteriaceae, with results in less than 24 h and excellent reproducibility across laboratories.

Original languageEnglish (US)
Pages (from-to)2321-2333
Number of pages13
JournalJournal of clinical microbiology
Volume55
Issue number8
DOIs
StatePublished - Aug 2017

All Science Journal Classification (ASJC) codes

  • Microbiology (medical)

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