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Possible physiological functions of penicillin-binding proteins in Staphylococcus aureus
Abstract:
There are four penicillin-binding proteins (PBPs) in Staphylococcus aureus, of which PBPs 2 and 3 are essential. Cefotaxime binds selectively to PBP 2, and cephalexin binds to PBP 3, each at its respective MIC. The morphology of S. aureus strains grown in the presence of the two antibiotics was examined by phase-contrast and scanning electron microscopy. Exposure of the cells to cefotaxime at concentrations at which it bound selectively to PBP 2 resulted in the extrusion of cytoplasm and cell lysis, whereas exposure to cephalexin at concentrations at which it bound exclusively to PBP 3 resulted in cell enlargement and the cessation of septation. The latter morphological response was very similar to that produced by norfloxacin. The results suggest that in S. aureus, PBP 2 may be the primary peptidoglycan transpeptidase, and PBP 3 may be involved in septation.
Insights
Cefotaxime and cephalexin target essential proteins in Staphylococcus aureus. Cefotaxime causes cell lysis by targeting PBP 2, while cephalexin causes cell enlargement by targeting PBP 3, suggesting distinct roles for these penicillin-binding proteins.
Area of Science:
- Microbiology
- Molecular Biology
- Biochemistry
Background:
- Staphylococcus aureus possesses four penicillin-binding proteins (PBPs), with PBPs 2 and 3 identified as essential for bacterial survival.
- Antibiotics like cefotaxime and cephalexin exhibit selective binding affinities to specific PBPs at their respective minimum inhibitory concentrations (MICs).
Purpose of the Study:
- To investigate the distinct roles of PBP 2 and PBP 3 in Staphylococcus aureus by examining cellular morphology following selective antibiotic exposure.
- To elucidate the functional involvement of PBP 2 and PBP 3 in peptidoglycan synthesis and cell division.
Main Methods:
- Utilizing phase-contrast and scanning electron microscopy to observe morphological changes in Staphylococcus aureus strains.
- Treating bacterial cultures with cefotaxime and cephalexin at concentrations targeting PBP 2 and PBP 3, respectively.
Main Results:
- Cefotaxime exposure, selectively targeting PBP 2, induced cytoplasm extrusion and cell lysis.
- Cephalexin exposure, selectively targeting PBP 3, resulted in cell enlargement and inhibited septation, mimicking norfloxacin's effect.
- These morphological changes indicate differential functions for PBP 2 and PBP 3.
Conclusions:
- Penicillin-binding protein 2 (PBP 2) in Staphylococcus aureus likely functions as the primary peptidoglycan transpeptidase.
- Penicillin-binding protein 3 (PBP 3) appears to play a crucial role in the septation process during cell division.
- The distinct morphological outcomes provide evidence for the specialized functions of PBP 2 and PBP 3 in bacterial cell wall metabolism and division.