Low-affinity penicillin-binding protein associated with beta-lactam resistance in Staphylococcus aureus
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Abstract:
Methicillin resistance in Staphylococcus aureus has been associated with alterations in the penicillin-binding proteins (PBPs). An intriguing property of all methicillin-resistant staphylococci is the dependence of resistance on the pH value of the growth medium. Growth of such bacteria at pH 5.2 completely suppressed the expression of methicillin resistance. We have examined the PBP patterns of methicillin-resistant staphylococci grown at pH 7.0. We detected a high-molecular-weight PBP (PBP-2a; approximate size, 78,000 daltons) that was only present in the resistant bacteria but not in the isogenic sensitive strain. In cultures grown at pH 5.2, the extra PBP was not detectable.
Insights
Methicillin resistance in Staphylococcus aureus depends on pH. A specific protein, PBP-2a, is crucial for resistance at neutral pH but absent at acidic pH 5.2.
Area of Science:
- Microbiology
- Molecular Biology
- Biochemistry
Background:
- Methicillin resistance in Staphylococcus aureus is linked to changes in penicillin-binding proteins (PBPs).
- Methicillin-resistant staphylococci exhibit a unique pH-dependent resistance mechanism.
Purpose of the Study:
- To investigate the role of penicillin-binding proteins (PBPs) in the pH-dependent methicillin resistance of Staphylococcus aureus.
- To identify specific PBPs associated with methicillin resistance.
Main Methods:
- Culturing methicillin-resistant and sensitive Staphylococcus aureus strains at different pH levels (pH 7.0 and pH 5.2).
- Analyzing penicillin-binding protein (PBP) patterns using gel electrophoresis.
Main Results:
- A high-molecular-weight PBP, designated PBP-2a (approx. 78,000 daltons), was detected in methicillin-resistant strains at pH 7.0.
- This unique PBP (PBP-2a) was absent in the isogenic sensitive strain.
- PBP-2a was not detectable in methicillin-resistant strains grown at pH 5.2, correlating with suppressed resistance.
Conclusions:
- The presence of PBP-2a is essential for expressing methicillin resistance in Staphylococcus aureus.
- Methicillin resistance is regulated by environmental pH, with PBP-2a expression being pH-sensitive.