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CRE Isolate Submission and Laboratory Testing - Minnesota Dept. of Health

CRE Isolate Submission and Laboratory Testing

The term CRE refers to carbapenem-resistant Enterobacteriaceae. Some CRE produce enzymes called carbapenemases that break apart carbapenems; these are referred to as carbapenemase-producing CRE (CP-CRE). Currently, the most common type of carbapenemase in the United States is the Klebsiella pneumoniae carbapenemase (KPC). In 2010, carbapenemases known as metallo-beta-lactamases (MBL) were first detected in the U.S. These include the New Delhi MBL (NDM),  Imipenemase (IMP), and Verona integron-encoded MBL (VIM). Another important emerging carbapenemase is OXA-48. The genes encoding carbapenemases are often located on plasmids that are easily spread between organisms.

It is important for laboratories to implement the current Clinical and Laboratory Standards Institute (CLSI) breakpoints for Enterobacteriaceae and carbapenems in order to appropriately identify CRE.

On this page:
Criteria for Submission of Isolates
Appropriate Specimen Types
Specimen submission forms
Shipping to MDH-PHL
Laboratory Testing for Carbapenemase-Producing CRE
Outbreak and surveillance testing
Other CRE laboratory information

Criteria for submission of isolates

  • Klebsiella spp., Enterobacter spp., Escherichia coli, and Citrobacter spp. isolates meeting the following CLSI breakpoints (current CLSI standard) should be reported and an isolate submitted to the MDH-PHL:
Antibiotic MIC (µg/mL)
Ertapenem ≥2, R
Imipenem ≥4, R
Meropenem ≥4, R
Doripenem ≥4, R

  • Isolates found to carry a carbapenemase enzyme (such as KPC) as demonstrated by testing methods such as polymerase chain reaction (PCR), modified Hodge test, etc.
  • Other Enterobacteriaceae spp. resistant to any carbapenem antibiotic can also be submitted to the MDH-PHL for further characterization

Appropriate specimen types

  • A pure, low passage CRE isolate is preferred as some carbapenem resistance mechanisms are plasmid-based and can be lost with multiple subcultures.
  • Submit isolate on a non-inhibitory, non-selective agar plate or slant (e.g. Sheep blood agar, Tryptic soy agar, etc.)

Specimen submission forms

MDH-PHL requests the following documentation to be included with each CRE isolate submission:

  • General Infectious Disease Laboratory Submission Form (PDF) (required):
    • Be sure to include the following information:
      • project number (1380)
      • patient information
      • specimen source
      • collection date
      • isolate genus/species
  • Antimicrobial Susceptibility Testing (AST) Report Printout (required):
    • Submit the raw data MIC profile obtained from your AST Instrument (i.e. Vitek2, Microscan, Phoenix)
    • Note: for manual Microscan users, a hand-written AST report is acceptable
  • CRE and CRPA Isolate - Supplemental Submission Form (PDF)
    (optional - print and fill out manually):
    • This form was created to allow MLS laboratories to record results for any CRE testing performed prior to isolate submission.
    • Results could include: Modified Hodge Test Results, Carbapenem E-test Results, Carbapenem Disk Diffusion Results, Select Antimicrobial Agent Results, and/or Results from Other Tests Performed (i.e. Carba NP, PCR)

Shipping to MDH-PHL

  • Ship specimens to MDH-PHL by an overnight delivery service or local courier.
    Note: It is the responsibility of the submitting laboratory to determine the appropriate packaging and shipping for patient specimens and culture isolates. See U.S. Department of Transportation Regulations: Hazardous materials shipping for more information.
  • Isolates can be shipped at either room temperature or with refrigeration.
  • Ship to:
    Minnesota Department of Health
    Public Health Laboratory
    Attn: Biological Accessioning
    601 Robert St. N
    St. Paul, Minnesota 55155-2531

Laboratory Testing for Carbapenemase-Producing CRE

MDH CRE outbreak and surveillance testing

  • MDH-PHL has the capacity to provide outbreak investigation testing for CP-CRE to Minnesota health care facilities, if necessary.
  • MDH-PHL can also provide guidance on outbreak detection protocols to be used in your facility. Call MDH Public Health Laboratory for consultation at 651-201-5073.


MDH-PHL Special Microbiology Laboratory is available during regular business hours for consultation on CRE testing and result interpretation (651-201-5073).

Updated Friday, 14-Oct-2022 15:23:04 CDT