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Penicillin-binding proteins as resistance determinants in clinical isolates of Streptococcus pneumoniae
P Reichmann1, A König, A Marton
1Max-Planck Institut für molekulare Genetik, Berlin, Germany.
Abstract:
Altered penicillin-binding proteins (PBPs) with reduced affinity for penicillin are encoded by mosaic genes in penicillin-resistant clinical isolates of Streptococcus pneumoniae. Generally, members of one bacterial clone contain the same mosaic gene. We report here on a serotype 19A clone of penicillin- and multiple-resistant S. pneumoniae prevalent in Hungary, members of which are exceptionally diverse in terms of PBP properties. The pbp2x gene of four 19A isolates was sequenced, and a distinct mosaic structure detected in each case. The pbp2x genes also differed from a homologous gene of a high-level penicillin-resistant S. mitis from Hungary. The contribution of PBPs to resistance development was studied on transformation experiments using the laboratory strain R6 as recipient, and PBP genes from the type 19A isolate Hu11. pbp2x and pbp2b function as primary resistance determinants for different beta-lactams. Secondary transformation with pbp1a increased the resistance level considerably for penicillins and cefotaxime. Chromosomal DNA of a high-level penicillin- and cefotaxime-resistant S. mitis from Hungary also transformed the R6 strain to increased resistance levels, and PBP2x and PBP2b functioned as primary resistance determinants as above. In contrast, high-level cefotaxime resistance appeared to be due to a low affinity PBP2a, indicating that this PBP can also function as a resistance determinant.
Insights
Penicillin-resistant Streptococcus pneumoniae clones exhibit diverse penicillin-binding protein (PBP) genes, unlike typical bacterial clones. This study reveals mosaic pbp2x gene variations within a single clone, impacting beta-lactam resistance.
Area of Science:
- Microbiology
- Genetics
- Molecular Biology
Background:
- Penicillin resistance in Streptococcus pneumoniae is often linked to altered penicillin-binding proteins (PBPs) encoded by mosaic genes.
- Typically, bacterial clones share identical mosaic genes, but this study investigates an exception.
Purpose of the Study:
- To investigate the genetic diversity of penicillin-binding protein (PBP) genes within a specific clone of multidrug-resistant Streptococcus pneumoniae.
- To determine the role of different PBPs in conferring resistance to beta-lactam antibiotics.
Main Methods:
- Sequencing of the pbp2x gene from four clinical isolates of a serotype 19A Streptococcus pneumoniae clone.
- Transformation experiments using the laboratory strain R6 with PBP genes from clinical isolates.
- Analysis of resistance levels conferred by different PBP gene combinations.
Main Results:
- Exceptional diversity in pbp2x mosaic gene structures was found within a single serotype 19A Streptococcus pneumoniae clone.
- pbp2x and pbp2b genes were identified as primary determinants for resistance to various beta-lactams.
- Secondary transformation with pbp1a significantly enhanced resistance to penicillins and cefotaxime.
- High-level cefotaxime resistance was associated with a low-affinity PBP2a.
Conclusions:
- A single clone of Streptococcus pneumoniae can harbor diverse PBP gene structures, challenging previous assumptions.
- Specific PBPs (PBP2x, PBP2b, and PBP2a) play crucial roles in determining resistance levels to beta-lactam antibiotics.