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Interaction of non-lytic beta-lactams with penicillin-binding proteins in Streptococcus pneumoniae
R Hakenbeck1, S Tornette, N F Adkinson
1Max-Planck-Institut für molekulare Genetik, Berlin, Germany.
Abstract:
The monobactam aztreonam and the cephalosporin ceftazidime, beta-lactam antibiotics that possess the same side chain R1, showed unusual effects on exponentially growing pneumococci compared to other beta-lactams. Both antibiotics did not induce lysis even at concentrations up to 2 mg ml-1, values well above the respective MICs. However, morphological alterations and growth inhibition of the cells were observed at much lower concentrations. Binding to penicillin-binding proteins (PBPs) in vitro could be monitored directly by using anti-aztreonam antiserum and the Western blot technique. Both antibiotics showed high affinity for PBP 3, but had an extremely low affinity for PBP 2b. It is suggested that the failure to bind to PBP 2b is responsible for the failure to induce lysis in pneumococci.
Insights
Aztreonam and ceftazidime, beta-lactam antibiotics, did not cause pneumococci lysis. These drugs bind to penicillin-binding protein 3 but not PBP 2b, explaining their unusual effect on bacterial growth and morphology.
Area of Science:
- Microbiology
- Bacteriology
- Pharmacology
Background:
- Beta-lactam antibiotics are crucial for treating bacterial infections.
- Pneumococci are significant human pathogens.
- Penicillin-binding proteins (PBPs) are essential bacterial enzymes targeted by beta-lactams.
Purpose of the Study:
- To investigate the unusual effects of aztreonam and ceftazidime on pneumococci.
- To determine the binding affinities of these antibiotics to specific PBPs.
- To elucidate the mechanism behind the lack of lysis induced by these drugs.
Main Methods:
- Monitoring antibiotic effects on exponentially growing pneumococci.
- Measuring antibiotic concentrations and Minimum Inhibitory Concentrations (MICs).
- Utilizing Western blot technique with anti-aztreonam antiserum to assess PBP binding.
Main Results:
- Aztreonam and ceftazidime did not induce lysis in pneumococci, even at high concentrations.
- Morphological alterations and growth inhibition were observed at lower concentrations.
- Both antibiotics exhibited high affinity for PBP 3 but very low affinity for PBP 2b.
Conclusions:
- The failure of aztreonam and ceftazidime to bind to PBP 2b is likely responsible for their inability to induce lysis in pneumococci.
- These findings provide insight into the specific PBP targets of beta-lactam antibiotics and their differential effects on bacterial cell division and morphology.