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Utilizing the Carba NP test as an indicator of expression level of carbapenemase genes in Enterobacteriaceae
Takaya Segawa1, Mari Matsui1, Masato Suzuki1
1Department of Bacteriology II, National Institute of Infectious Diseases, Musashimurayama, Tokyo, Japan.
Abstract:
The Carba NP test was developed to detect carbapenemase-producing Enterobacteriaceae, and uses imipenem as the reaction substrate. In Japan, IMP-6 metallo-β-lactamase (MBL) producers, which are usually resistant to meropenem but susceptible to imipenem, and IMP-1 MBL producers, which are usually resistant to both carbapenems are prevalent. We performed the Carba NP test with IMP-6 and IMP-1 MBL producers, and both types were detected by the Carba NP test with high sensitivity. All IMP-1 MBL producers were detected by the Carba NP test, but the minimum inhibitory concentrations (MICs) of imipenem varied from 0.25 to >32μg/mL, and the time to positivity varied from 0 to 30min. Time to positivity was significantly correlated with expression levels of blaIMP-1, but not with MICs of imipenem. These results suggested that the Carba NP test can be used as a screening assay for carbapenemase gene expression levels among producers of the same type of carbapenemase. Using this approach, it is possible to determine whether the carbapenem resistance of each carbapenemase-producing Enterobacteriaceae isolate is primarily due to carbapenemase production, or to another mechanism such as outer membrane impermeability.
Insights
The Carba NP test effectively detects carbapenemase-producing Enterobacteriaceae, including IMP-6 and IMP-1 metallo-β-lactamase producers. Test positivity correlates with carbapenemase gene expression, aiding resistance mechanism identification.
Area of Science:
- Clinical microbiology
- Antimicrobial resistance
- Molecular diagnostics
Background:
- Carbapenemase-producing Enterobacteriaceae (CPE) pose a significant global health threat.
- Prevalence of IMP-6 and IMP-1 metallo-β-lactamase (MBL) producers in Japan necessitates accurate detection methods.
- The Carba NP test utilizes imipenem to detect carbapenemase production.
Purpose of the Study:
- To evaluate the Carba NP test's sensitivity for detecting prevalent IMP-6 and IMP-1 MBL producers in Japan.
- To investigate the correlation between Carba NP test results and carbapenemase gene expression levels.
- To assess the utility of the Carba NP test in differentiating carbapenem resistance mechanisms.
Main Methods:
- The Carba NP test was performed on Enterobacteriaceae isolates producing IMP-6 and IMP-1 metallo-β-lactamases.
- Sensitivity of the Carba NP test was assessed for both MBL types.
- Minimum inhibitory concentrations (MICs) of imipenem and time to positivity were recorded.
- Correlation between time to positivity and blaIMP-1 expression levels was analyzed.
Main Results:
- The Carba NP test demonstrated high sensitivity in detecting both IMP-6 and IMP-1 MBL producers.
- All IMP-1 MBL producers were detected, with varying imipenem MICs and times to positivity.
- Time to positivity showed a significant correlation with blaIMP-1 gene expression levels.
- No significant correlation was found between time to positivity and imipenem MICs.
Conclusions:
- The Carba NP test is a sensitive tool for detecting IMP-6 and IMP-1 MBL-producing Enterobacteriaceae.
- The test can serve as a screening assay for carbapenemase gene expression levels within specific MBL types.
- This approach aids in distinguishing carbapenem resistance due to carbapenemase production versus other mechanisms like outer membrane impermeability.
