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Genetic basis of methicillin resistance in Staphylococcus aureus
1Institute of Medical Microbiology, University of Zürich, Postfach, Switzerland. bberger@immv.unizh.ch
Abstract:
Methicillin resistance in staphylococci is due to the acquisition of the mecA gene encoding a new penicillin-binding protein (PBP2', PBP2a) that has a lower affinity to methicillin than the endogenous PBPs. PBP2' is involved in the assembly of the cell wall peptidoglycan in the presence of high concentrations of beta-lactams that otherwise inhibit the endogenous PBPs. The production of PBP2' is under dual control by its own mecR1-mecI- and the penicillinase blaR1-blaI-encoded regulatory elements. Resistance to high levels of methicillin depends, in addition to PBP2', on chromosomally encoded factors that are involved in the synthesis and degradation of the peptidoglycan. Any mutations that reduce peptidoglycan precursor formation or change the chemical composition of the muropeptide precursor result in lowered resistance.
Insights
Methicillin resistance in staphylococci arises from the mecA gene, producing penicillin-binding protein PBP2a. This altered protein, along with other factors, enables staphylococci to resist beta-lactam antibiotics.
Area of Science:
- Microbiology
- Molecular Biology
- Biochemistry
Background:
- Staphylococci exhibit methicillin resistance primarily through the acquisition of the mecA gene.
- This gene encodes a novel penicillin-binding protein (PBP2a) with reduced affinity for methicillin compared to native PBPs.
Purpose of the Study:
- To elucidate the molecular mechanisms underlying methicillin resistance in staphylococci.
- To understand the role of PBP2a and regulatory elements in antibiotic resistance.
Main Methods:
- Analysis of the mecA gene and its encoded PBP2a.
- Investigation of regulatory pathways (mecR1-mecI and blaR1-blaI) controlling PBP2a production.
- Examination of peptidoglycan synthesis and degradation pathways.
Main Results:
- PBP2a is crucial for cell wall peptidoglycan assembly in the presence of beta-lactams, which inhibit endogenous PBPs.
- PBP2a production is regulated by both mecR1-mecI and blaR1-blaI systems.
- High-level methicillin resistance requires PBP2a and additional chromosomally encoded factors influencing peptidoglycan metabolism.
Conclusions:
- Methicillin resistance in staphylococci is a multifactorial trait involving PBP2a and intricate regulation of cell wall synthesis.
- Alterations in peptidoglycan precursor formation or composition significantly impact resistance levels.