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Penicillin-binding protein 2b of Streptococcus pneumoniae in piperacillin-resistant laboratory mutants
R Hakenbeck1, C Martin, C Dowson
1Max-Planck Institut für Molekulare Genetik, Berlin, Germany.
Abstract:
In Streptococcus pneumoniae, alterations in penicillin-binding protein 2b (PBP 2b) that reduce the affinity for penicillin binding are observed during development of beta-lactam resistance. The development of resistance was now studied in three independently obtained piperacillin-resistant laboratory mutants isolated after several selection steps on increasing concentrations of the antibiotic. The mutants differed from the clinical isolates in major aspects: first-level resistance could not be correlated with alterations in the known PBP genes, and the first PBP altered was PBP 2b. The point mutations occurring in the PBP 2b genes were characterized. Each mutant contained one single point mutation in the PBP 2b gene. In one mutant, this resulted in a mutation of Gly-617 to Ala within one of the homology boxes common to all PBPs, and in the other two cases, the same Gly-to-Asp substitution at the end of the penicillin-binding domain had occurred. The sites affected were homologous to those determined previously in the S. pneumoniae PBP 2x of mutants resistant to cefotaxime, indicating that, in both PBPs, similar sites are important for interaction with the respective beta-lactams.
Insights
Mutations in penicillin-binding protein 2b (PBP 2b) drive piperacillin resistance in Streptococcus pneumoniae. Specific point mutations in PBP 2b alter antibiotic binding, contributing to beta-lactam resistance development.
Area of Science:
- Microbiology
- Molecular Biology
- Antibiotic Resistance
Background:
- Beta-lactam antibiotics, including piperacillin, are crucial for treating Streptococcus pneumoniae infections.
- Development of resistance in S. pneumoniae is often linked to alterations in penicillin-binding proteins (PBPs).
- Penicillin-binding protein 2b (PBP 2b) is implicated in reduced affinity for penicillin, a key factor in resistance.
Purpose of the Study:
- To investigate the genetic basis of piperacillin resistance in Streptococcus pneumoniae.
- To characterize the specific mutations in PBP 2b responsible for acquired resistance.
- To compare resistance mechanisms with those observed for other beta-lactams.
Main Methods:
- Isolation and characterization of three independent piperacillin-resistant laboratory mutants of S. pneumoniae.
- Genetic analysis to identify point mutations within the PBP 2b gene.
- Determination of the specific amino acid substitutions resulting from these mutations.
Main Results:
- Each resistant mutant possessed a single point mutation in the PBP 2b gene.
- Identified mutations included Gly-617 to Ala and Gly-to-Asp substitutions in critical regions of PBP 2b.
- These altered sites are homologous to those previously identified in PBP 2x associated with cefotaxime resistance.
Conclusions:
- Single point mutations in PBP 2b are sufficient to confer piperacillin resistance in S. pneumoniae.
- Specific amino acid changes in PBP 2b directly impact its interaction with beta-lactam antibiotics.
- Similar mutation sites in different PBPs (PBP 2b and PBP 2x) suggest conserved mechanisms of beta-lactam interaction and resistance.