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[Interpretative reading of the non-fermenting gram-negative bacilli antibiogram]
1Servicio de Microbiología, Institut d'Infeccions i Immunologia, Hospital Clínic i Provincial, Barcelona, España. jvilaestape@yahoo.com
Enfermedades Infecciosas Y Microbiologia Clinica
|June 27, 2002
Summary
Multidrug resistance in key Gram-negative bacteria like Pseudomonas aeruginosa is driven by beta-lactamases, altered permeability, and efflux pumps. Mechanisms in Acinetobacter baumannii and Stenotrophomonas maltophilia also contribute to treatment challenges.
Area of Science:
- Clinical microbiology
- Antimicrobial resistance mechanisms
- Molecular biology
Background:
- Non-fermenting Gram-negative rods, including Pseudomonas aeruginosa, Acinetobacter baumannii, and Stenotrophomonas maltophilia, are significant clinical pathogens often exhibiting multidrug resistance.
- Understanding resistance mechanisms is crucial for effective antimicrobial therapy.
Purpose of the Study:
- To review and summarize the primary mechanisms of antimicrobial resistance in Pseudomonas aeruginosa, Acinetobacter baumannii, and Stenotrophomonas maltophilia.
- To highlight the challenges in interpreting antimicrobial susceptibility testing for these organisms.
Main Methods:
- Literature review of established resistance mechanisms.
- Analysis of genetic and biochemical factors contributing to resistance.
- Comparison of resistance pathways across the three bacterial species.
Main Results:
- Pseudomonas aeruginosa exhibits resistance to beta-lactams via beta-lactamases, altered permeability (e.g., OprD loss), and efflux pumps (MexAB-OprM). Aminoglycoside resistance is mainly due to inactivating enzymes and the MexXY-OprM pump. Quinolone resistance involves topoisomerase changes, permeability alterations, and efflux.
- Acinetobacter baumannii resistance mechanisms are less characterized but involve beta-lactamases, altered penicillin-binding proteins, modifying enzymes (aminoglycosides), and target alterations (quinolones).
- Stenotrophomonas maltophilia displays carbapenem and beta-lactam resistance due to L-1 and L-2 beta-lactamases, with aminoglycoside resistance linked to modifying enzymes. Quinolone resistance is primarily mediated by active efflux.
Conclusions:
- Multidrug resistance in these Gram-negative pathogens is multifactorial, involving enzymatic inactivation, target modification, altered cellular permeability, and active efflux systems.
- The diverse and sometimes poorly understood resistance mechanisms necessitate ongoing research and careful interpretation of antibiotic susceptibility data for optimal patient management.