Test ID: KPCRP
KPC (blaKPC) in Enterobacteriaceae, Molecular Detection, PCR
Useful For 
Suggests clinical disorders or settings where the test may be helpful
Assessing pure isolates of Klebsiella pneumoniae or other members of the Enterobacteriaceae for carbapenem resistance
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Resistance to carbapenem antibiotics, by means of the enzyme KPC (Klebsiella pneumoniae carbapenemase), produced by Klebsiella pneumoniae and other members of the Enterobacteriaceae family, is becoming more common. The gene blaKPC encodes KPC production.
In addition to KPC production, several other genetic factors can cause resistance to carbapenems including production of other carbapenemases, plasmid-encoded AmpC beta-lactamases, or extended beta-lactamase (ESBL) combined with decreased membrane permeability. It is important to know if an isolate is resistant to carbapenems for proper reporting of antimicrobial susceptibility results and, in turn, determining proper antimicrobial therapy.
Detection of carbapenemases by the conventional phenotypic method (ie, modified Hodge test) may be subjective and is not rapid. Testing for the minimum inhibitory concentration (MIC) determines the level of resistance of the isolate, but not the mechanism causing the resistance. Real-time PCR is a sensitive, specific, and rapid means of detecting of a specific portion of the gene encoding KPC production.
Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.
Not applicable
Interpretation Provides information to assist in interpretation of the test results
A positive KPC (Klebsiella pneumoniae carbapenemase) PCR indicates that the isolate tested carries blaKPC. Carbapenems (doripenem, ertapenem, imipenem, meropenem) should not be used to treat these isolates.
A negative result indicates the absence of detectable DNA, however false negative results may occur due to inhibition of PCR or sequence variability underlying primers and/or probes.
The assay detects the 13 blaKPC genotypes described as of June 2012.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
This assay should only be used for testing of isolates. The use of this assay as a screening test directly from clinical specimens (eg, rectal swabs) has not been evaluated.
There are other mechanisms of carbapenem resistance beyond KPC-type carbapenemases that may confer resistance to carbapenems.
Loss of a plasmid carrying a resistance gene with serial passage and rarely on primary culture or in vivo, may result in non-detection of plasmid-mediated resistance.
The assay detects genes which typically confer carbapenem resistance; lack of phenotypic expression of that gene may result in a positive PCR result in a carbapenem susceptible isolate.
Supportive Data
The accuracy of this assay focused on comparison of 17 isolates that were tested by both the Centers for Disease Control and Prevention (CDC) assay and Mayo assay. The 17 specimens consisted of 5 positive isolates received from outside clients, a positive control isolate and negative control isolate shared by CDC for validation purposes, and 10 isolates (8 positive and 2 negatives) that were sent to Mayo as a blinded challenge by CDC. Three of the 5 positive isolates from clients were sent to CDC for confirmation. The remaining 2 were confirmed by modified Hodge testing (gold standard) by the Mayo Clinic Bacteriology Development team.
The results of the comparisons are as follows:
| KPC Assay | CDC | ||
| POS | NEG | ||
| Mayo | POS | 14 | 0 |
| NEG | 0 | 3 | |
In addition to the confirmation testing of positives (the retrospective examination of the 17 specimens above), an additional 17 isolates from a separate ESBL study were subjected to the modified Hodge testing for carbapenemase production. The additional 17 isolates were also tested using the KPC LightCycler assay. Results of the retrospective comparison are as follows:
| Method | Modified Hodge | ||
| POS | NEG | ||
| KPC | POS | 15 | 0 |
| NEG | 0 | 19 | |
To supplement the above studies, an additional 20 Enterobacteriacae isolates (15 positive, 5 negative) were tested in a blinded manner by the KPC PCR assay, the CDC KPC assay, and modified Hodge test. All results were as expected with no discordant results among the 2 PCR assays and the modified Hodge test.
Clinical Reference Provides recommendations for further in-depth reading of a clinical nature
1. Real-Time PCR Procedure for Detection of Genes Encoding KPC Carbapenemases. Centers for Disease Control and Prevention 2007.(unpublished)
2. CLSI Document M100-S19, Vol 29, No.3, 2009. CLSI, Wayne, PA
3. Anderson KF, Lonsway DR, Rasheed JK, et al: Evaluation of methods to identify the Klebsiella pneumoniae carbapenemase in Enterobacteriaceae. J Clin Microbiol 2007;45(8):2723-2725
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