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Phenotypic detection of metallo-β-lactamase in imipenem-resistant Pseudomonas aeruginosa
Yalda Khosravi1, Mun Fai Loke, Eng Guan Chua
1Department of Medical Microbiology, University of Malaya, 50603 Kuala Lumpur, Malaysia.
Abstract:
Carbapenems are the primary choice of treatment for severe Pseudomonas aeruginosa infection. However, the emergence of carbapenem resistance due to the production of metallo-β-lactamases (MBLs) is of global concern. In this study, 90 imipenem- (IPM- or IP-) resistant P. aeruginosa (IRPA) isolates, including 32 previously tested positive and genotyped for MBL genes by PCR, were subjected to double-disk synergy test (DDST), combined disk test (CDT), and imipenem/imipenem-inhibitor (IP/IPI) E-test to evaluate their MBLs detection capability. All three methods were shown to have a sensitivity of 100%. However, DDST was the most specific of the three (96.6%), followed by IP/IPI E-test interpreted based on the single criteria of IP/IPI ≥8 as positive (62.1%), and CDT was the least specific (43.1%). Based on the data from this evaluation, we propose that only IRPA with IP MIC >16 μg/mL and IP/IPI ≥8 by IP/IPI E-test should be taken as positive for MBL activity. With the new dual interpretation criteria, the MBL IP/IPI E-test was shown to achieve 100% sensitivity as well as specificity for the IRPA in this study. Therefore, the IP/IPI E-test is a viable alternative phenotypic assay to detect MBL production in IRPA in our population in circumstances where PCR detection is not a feasible option.
Insights
Metallo-β-lactamase (MBL) detection in carbapenem-resistant Pseudomonas aeruginosa is crucial. The imipenem/imipenem-inhibitor (IP/IPI) E-test, with new dual criteria, offers 100% sensitivity and specificity for MBL detection.
Area of Science:
- Microbiology
- Infectious Diseases
- Antimicrobial Resistance
Background:
- Carbapenems are vital for treating severe Pseudomonas aeruginosa infections.
- Metallo-β-lactamase (MBL) production is a growing global concern, leading to carbapenem resistance.
- Accurate phenotypic detection of MBLs in P. aeruginosa is essential for guiding treatment.
Purpose of the Study:
- To evaluate the MBL detection capability of three phenotypic methods: double-disk synergy test (DDST), combined disk test (CDT), and imipenem/imipenem-inhibitor (IP/IPI) E-test.
- To propose optimized interpretation criteria for the IP/IPI E-test to improve its specificity.
- To assess the utility of the IP/IPI E-test as a viable alternative to PCR for MBL detection.
Main Methods:
- Ninety imipenem-resistant P. aeruginosa (IRPA) isolates were tested.
- Phenotypic detection of MBL activity was performed using DDST, CDT, and IP/IPI E-test.
- Isolates were also genotyped for MBL genes via PCR (for comparison).
Main Results:
- All three phenotypic methods demonstrated 100% sensitivity for MBL detection.
- DDST showed the highest specificity (96.6%), followed by IP/IPI E-test (62.1%) with single criteria, and CDT (43.1%).
- The proposed dual interpretation criteria (IP MIC >16 μg/mL and IP/IPI ≥8) for the IP/IPI E-test achieved 100% sensitivity and specificity.
Conclusions:
- The IP/IPI E-test, when interpreted using the novel dual criteria, is a highly accurate phenotypic method for detecting MBL production in IRPA.
- This optimized IP/IPI E-test provides a valuable alternative to PCR in settings where molecular detection is not feasible.
- Accurate and timely MBL detection is critical for managing severe Pseudomonas aeruginosa infections.
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