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Carbapenem resistance mechanisms in Pseudomonas aeruginosa clinical isolates
1Division of Infectious Disease, Department of Internal Medicine, College of Medicine, University of Dankook, Chonan, Seoul, Korea. paihj@unitel.co.kr
Abstract:
In order to define the contributions of the mechanisms for carbapenem resistance in clinical strains of Pseudomonas aeruginosa, we investigated the presence of OprD, the expressions of the MexAB-OprM and MexEF-OprN systems, and the production of the beta-lactamases for 44 clinical strains. All of the carbapenem-resistant isolates showed the loss of or decreased levels of OprD. Three strains overexpressed the MexAB-OprM efflux system by carrying mutations in mexR. These three strains had the amino acid substitution in MexR protein, Arg (CGG) --> Gln (CAG), at the position of amino acid 70. None of the isolates, however, expressed the MexEF-OprN efflux system. For the characterization of beta-lactamases, at least 13 isolates were the depressed mutants, and 12 strains produced secondary beta-lactamases. Based on the above resistance mechanisms, the MICs of carbapenem for the isolates were analyzed. The MICs of carbapenem were mostly determined by the expression of OprD. The MICs of meropenem were two- to four-fold increased for the isolates which overexpressed MexAB-OprM in the background of OprD loss. However, the elevated MICs of meropenem for some individual isolates could not be explained. These findings suggested that other resistance mechanisms would play a role in meropenem resistance in clinical isolates of P. aeruginosa.
Insights
Carbapenem resistance in Pseudomonas aeruginosa is primarily linked to OprD loss. Overexpression of the MexAB-OprM efflux system and beta-lactamase production also contribute to resistance, with other mechanisms potentially involved.
Area of Science:
- Microbiology
- Molecular Biology
- Antimicrobial Resistance
Background:
- Pseudomonas aeruginosa is a significant opportunistic pathogen.
- Carbapenem antibiotics are crucial for treating multidrug-resistant bacterial infections.
- Understanding carbapenem resistance mechanisms in P. aeruginosa is vital for effective treatment strategies.
Purpose of the Study:
- To investigate the key mechanisms contributing to carbapenem resistance in clinical Pseudomonas aeruginosa isolates.
- To correlate specific genetic and protein expression changes with carbapenem minimum inhibitory concentrations (MICs).
Main Methods:
- Analysis of OprD presence and expression levels.
- Investigation of MexAB-OprM and MexEF-OprN efflux system expression via mutations in regulatory genes (e.g., mexR).
- Characterization of beta-lactamase production.
- Determination of carbapenem MICs for 44 clinical isolates.
Main Results:
- All carbapenem-resistant isolates exhibited loss or reduced levels of OprD.
- Three strains overexpressed MexAB-OprM due to mexR mutations (Arg70Gln substitution).
- No isolates expressed the MexEF-OprN system; however, 13 isolates showed depressed beta-lactamase mutants and 12 produced secondary beta-lactamases.
- OprD expression was the primary determinant of carbapenem MICs, with MexAB-OprM overexpression further increasing meropenem MICs two- to four-fold in OprD-deficient strains.
Conclusions:
- Loss of OprD is a major mechanism for carbapenem resistance in P. aeruginosa.
- MexAB-OprM efflux system overexpression and beta-lactamase production are significant contributing factors.
- Unexplained elevated meropenem MICs suggest the involvement of additional, yet unidentified, resistance mechanisms in clinical P. aeruginosa isolates.