CPE – Carbapenemase Producing Enterobacterales – Confirmation

Consistent with O. Reg. 671/92 of the French Language Services Act, laboratory testing information on this page is only available in English because it is scientific or technical in nature and is for use only by qualified health care providers and not by members of the public.

Background
This page provides testing information for isolates that belongs to Enterobacterales submitted to Public Health Ontario’s (PHO) Laboratory to confirm the ability to produce carbapenemases. Testing is done via phenotypic modified carbapenem inactivation method (mCIM) and multiplex real time PCR assay. For information regarding other testing options, refer to the following PHO webpages: Bacterial Cultures-Aerobic-Reference Identification/Confirmation

Updates
Alignment of reporting instruction for CPE -positive specimen to the Medical Officer of Health as per the Ontario Health Protection and Promotion Act

*Uncontrolled print copy. Valid only on day of print: 30 June 2024.

Testing Indications

Identifying carbapenem resistance among isolates that are members of Enterobacterales is needed to support infection prevention efforts and antimicrobial stewardship in order to reduce the spread of these isolates among patients.
Surveillance for carbapenem resistance is essential at the population level to assess trends in the incidence of these organisms, evaluate the success of prevention efforts, and provide guidance for the treatment of infections.
Presumptive carbapenemase-producing isolates that are members of Enterobacterales must be submitted to PHO’s laboratory for confirmation.

Acceptance/Rejection Criteria

Primary specimens are not acceptable. Only pure cultures are accepted for carbapenem resistance testing.
Mixed or non-viable cultures will not be tested. A written report will be issued to indicate that the test has been rejected.
Mislabelled or unlabelled cultures will not be tested. A report will be sent to the submitting laboratory stating “Culture received un-labelled” or “Requisition identification does not match the identification information on the culture received. Please resubmit if required.”

Specimen Collection and Handling

Specimen Requirements

Test Requested

Required Requisition(s)

Specimen Type

Minimum Volume

Collection Kit

CPE –
Carbapenemase producing
Enterobacterales

Reference Bacteriology Requisition

pure viable subculture of organism on appropriate medium (Columbia sheep blood agar plate) OR

a swab of a pure subculture of the organism in Amies transport medium

N/A

Submission and Collection Notes

Complete all fields on the Reference Bacteriology Requisition including:

Test(s) requested
Date of primary specimen collection
Primary source of isolation (mandatory)
Culture information (presumptive identification, gram morphology, catalase, oxidase)
Clinical/epidemiology information
The number of consecutive blood cultures positive for the submitted isolate when isolates are from blood cultures
Contact information

Isolates must be submitted with the susceptibility profile including carbapenems tested, the organism identification and result of any phenotypic testing for carbapenemase production if available.

Primary specimens are unacceptable; they should be processed in the originating lab. A report will be issued to indicate that the test has been rejected.

Label the isolate’s culture plate or swab with the patient’s first and last name, date of collection, and one other unique identifier such as the patient’s date of birth or Health Card Number. For additional information see: Criteria for Acceptance of Patient Specimens. Failure to provide required information on the label may result in rejection or testing delay.

Isolates grown from screening specimens related to hospital infection control programs and outbreak investigations will also be accepted for confirmation of carbapenemase activity.

Limitations

Since carbapenemase production testing is performed only on Enterobacterales, when the identification of the isolate is unknown, confirmation of the isolate’s identification is performed first. If the identification is confirmed, carbapenemase testing will proceed.

Storage and Transport

Place culture in biohazard bag and seal. Store at 2-8°C while awaiting shipping. Specimens should be stored at 2-8°C following collection and shipped to PHO’s laboratory within 48 hours of isolation. All clinical specimens must be shipped in accordance to the Transportation of Dangerous Good Act.

Requisitions and Kit Ordering

Test Frequency and Turnaround Time (TAT)

CPE confirmation testing TAT is up to 3 days after receipt at PHO’s Laboratory-Toronto.

CPE PCR testing is performed 4 times per week at PHO’s laboratory-Toronto.

For isolates sent to National Microbiology Laboratory (NML) for further antimicrobial resistance testing when needed as per algorithm, 6 calendar days turnaround time from the time the isolate was received at NML should be considered.

STAT and Critical Specimens Testing

STAT testing is not available; however, for urgent samples (i.e. critical) please notify customer service to ensure the sample is on the next available run.

Test Methods

The modified carbapenem inactivation method (mCIM) test allows for the detection of carbapenemase in Enterobacterales as well as in Pseudomonas aeruginosa. It has been described as a highly robust phenotypic screening method that can reliably detect carbapenemase activity. ²

The multiplex real time PCR procedure includes 2 separate multiplex reactions, involving oligonucleotide primers and dual-labeled hydrolysis (Taqman) probes to be used in real-time PCR assays for the detection of Carbapenem-resistance genes among gram-negative bacteria. PHO’s laboratory is currently testing for the detection of KPC, NDM, GES, OXA-48-LIKE, VIM and IMP genes.

Algorithm

If Meropenem MIC is ≤0.12 mg/L and Ertapenem MIC is ≤0.5 mg/L and mCIM test is negative, Report as “Carbapenem MIC values do NOT suggest carbapenmase activity. Further testing was not performed”. PCR is not performed if Meropenem MIC is ≤0.12 mg/L, Ertapenem MIC is ≤0.5 mg/L and mCIM result is negative.
If either mCIM is positive or Inconclusive or Meropenem and/or Ertapenem values are above the cut-off, proceed to PCR for CPE gene testing.
If mCIM is positive and there is no carbapenemase gene detected, the isolate is sent to National Microbiology Laboratory for further antimicrobial resistance testing to detect beta-lactamase and carbapenemase genes.

Interpretation

The following table provides possible test results with associated interpretations:

mCIM result	PCR result	Interpretation
Positive or Inconclusive or Negative	[Name of gene(s)] detected	Positive
Negative or Inconclusive	No Carbapenemase genes detected	Negative with comment: PHOL is currently testing for the detection of KPC, NDM, GES, OXA-48-LIKE, VIM and IMP genes.
Positive	Carbapenemase gene not detected	Send specimen to NML for further antimicrobial resistance testing.

Reporting

CPE test result is reported as :

Carbapenemase detected (not detected ) by phenotypic method,
Name of the Carbapenemase gene(s) detected by molecular method.

Results are reported to the physician, authorized health care provider (General O. Reg 45/22, s.18) or submitter as indicated on the requisition.

Isolates that are confirmed as carbapenemase-producing are reported to the Medical Officer of Health as per Health Protection and Promotion Act.

References

CLSI Performance Standards for Antimicrobial Susceptibility Testing 29th Edition. M100.
Kim van der Zwaluw, et al, 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. PLOS ONE (DOI:10.1371/journal.pone.0123690) March 23, 2015