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Intra- and inter-specific transformation of Streptococcus pneumoniae to penicillin resistance
1Emergent Pathogen Research Unit, South African Medical Research Council, School of Pathology, Johannesburg.
Abstract:
Transformation studies were carried out with a penicillin susceptible (MIC 0.006 mg/l) laboratory strain of Streptococcus pneumoniae as recipient. Donor DNA was prepared from two clinical isolates of S. pneumoniae, four isolates of S. mitior and five isolates of S. sanguis. DNA from both isolates of S. pneumoniae generated penicillin-resistant transformants (MICs 0.03-2.0 mg/l). In addition, one isolate each of S. mitior and S. sanguis transformed the recipient to increased penicillin resistance, with MICs of 0.125 mg/l. DNA from the S. sanguis strain generated a transformant which showed a reduction in the penicillin-binding affinity of penicillin-binding protein (PBP) 2B. DNA from a second S. mitior strain generated intermediately resistant (MIC 0.5 mg/l) transformants in a single transformation round. The PBP profiles of these transformants showed an apparent molecular size alteration of PBP 2B, corresponding to a PBP found in the donor strain, and PBP 1B was no longer detected. Isolates of S. pneumoniae may apparently develop penicillin resistance either intrinsically, by intragenetic transfer, or by transfer of penicillin resistance determinants from viridans streptococci.
Insights
Penicillin resistance in Streptococcus pneumoniae can arise from intrinsic factors or transfer from other streptococci. This study shows genetic transfer from S. mitior and S. sanguis can confer penicillin resistance.
Area of Science:
- Microbiology
- Genetics
- Molecular Biology
Background:
- Penicillin resistance is a growing public health concern.
- Streptococcus pneumoniae is a significant human pathogen.
- Understanding resistance mechanisms is crucial for effective treatment.
Purpose of the Study:
- To investigate the genetic basis of penicillin resistance in Streptococcus pneumoniae.
- To determine if penicillin resistance determinants can be transferred from other streptococcal species.
- To identify specific genetic alterations associated with penicillin resistance.
Main Methods:
- Transformation studies using a penicillin-susceptible Streptococcus pneumoniae recipient strain.
- Donor DNA sourced from clinical isolates of S. pneumoniae, S. mitior, and S. sanguis.
- Analysis of penicillin minimum inhibitory concentrations (MICs) and penicillin-binding protein (PBP) profiles in transformants.
Main Results:
- Penicillin-resistant transformants were generated using DNA from S. pneumoniae, S. mitior, and S. sanguis.
- Transfer of resistance from S. mitior and S. sanguis increased penicillin resistance in recipient strains.
- Specific alterations in penicillin-binding protein 2B were observed, linked to reduced binding affinity and altered molecular size.
Conclusions:
- Streptococcus pneumoniae can acquire penicillin resistance through intrinsic mechanisms or horizontal gene transfer.
- Viridans streptococci, including S. mitior and S. sanguis, can serve as donors of penicillin resistance genes.
- Alterations in PBP 2B are a key mechanism conferring penicillin resistance in S. pneumoniae.