title: Modified Carbapenem Inactivation Method for Phenotypic Detection of Carbapenemase Production among Enterobacteriaceae.
abstract: The ability of clinical microbiology laboratories to reliably detect carbapenemase-producing carbapenem-resistantEnterobacteriaceae(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 familyEnterobacteriaceaethat 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 forEnterobacteriaceae, with results in less than 24 h and excellent reproducibility across laboratories.
authors.affiliation: Department of Pathology, Massachusetts General Hospital, Boston, Massachusetts, USA vmpierce@mgh.harvard.edu.
authors.forename: Virginia M
authors.initials: VM
authors.lastname: Pierce
authors.affiliation: Department of Pathology, Johns Hopkins Medical Institutions, Baltimore, Maryland, USA.
authors.forename: Patricia J
authors.initials: PJ
authors.lastname: Simner
authors.affiliation: Division of Healthcare Quality Promotion, Centers for Disease Control and Prevention, Atlanta, Georgia, USA.
authors.forename: David R
authors.initials: DR
authors.lastname: Lonsway
authors.affiliation: Beckman Coulter Diagnostics, Inc., West Sacramento, California, USA.
authors.forename: Darcie E
authors.initials: DE
authors.lastname: Roe-Carpenter
authors.affiliation: Department of Pathology, University of Maryland School of Medicine, Baltimore, Maryland, USA.
authors.forename: J Kristie
authors.initials: JK
authors.lastname: Johnson
authors.affiliation: BD Life Sciences-Diagnostic Systems, Sparks, Maryland, USA.
authors.forename: William B
authors.initials: WB
authors.lastname: Brasso
authors.affiliation: Department of Pathology and Laboratory Medicine, Lifespan Academic Medical Center, Providence, Rhode Island, USA.
authors.forename: April M
authors.initials: AM
authors.lastname: Bobenchik
authors.affiliation: Beckman Coulter Diagnostics, Inc., West Sacramento, California, USA.
authors.forename: Zabrina C
authors.initials: ZC
authors.lastname: Lockett
authors.affiliation: Department of Pathology, University of Chicago Medical Center, Chicago, Illinois, USA.
authors.forename: Angella
authors.initials: A
authors.lastname: Charnot-Katsikas
authors.affiliation: Department of Pathology, Massachusetts General Hospital, Boston, Massachusetts, USA.
authors.forename: Mary Jane
authors.initials: MJ
authors.lastname: Ferraro
authors.affiliation: Department of Pathology, NorthShore University HealthSystem, Evanston, Illinois, USA.
authors.forename: Richard B
authors.initials: RB
authors.lastname: Thomson
authors.affiliation: Department of Pathology and Laboratory Medicine, Weill-Cornell Medical College, New York, New York, USA.
authors.forename: Stephen G
authors.initials: SG
authors.lastname: Jenkins
authors.affiliation: Division of Healthcare Quality Promotion, Centers for Disease Control and Prevention, Atlanta, Georgia, USA.
authors.forename: Brandi M
authors.initials: BM
authors.lastname: Limbago
authors.affiliation: Department of Pathology, NorthShore University HealthSystem, Evanston, Illinois, USA.
authors.forename: Sanchita
authors.initials: S
authors.lastname: Das
mesh_terms: D001426:Bacterial Proteins / Q000032:analysis* / Q000378:metabolism; D015780:Carbapenems / Q000378:metabolism / Q000494:pharmacology*; D004755:Enterobacteriaceae / Q000201:enzymology*; D006801:Humans; D006868:Hydrolysis; D008826:Microbial Sensitivity Tests / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D001618:beta-Lactamases / Q000032:analysis* / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D015780:Carbapenems; D001618:beta-Lactamases; C063912:carbapenemase
keywords: Enterobacteriaceae; antimicrobial susceptibility testing; bacterial antibiotic resistance; bacteriological techniques; carbapenemase; carbapenems