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Drastic changes in the peptidoglycan composition of penicillin resistant laboratory mutants of Streptococcus
A Severin1, M V Vaz Pato, A M Sá Figueiredo
1Rockefeller University, New York NY 10021, USA.
Abstract:
The penicillin MIC of 2 Streptococcus pneumoniae clinical isolates was increased 100-fold (from 0.02 to 2.0 micromilligrams) and 20-fold (from 0.5 to 10.0 micromilligrams) through gradual exposure of the bacteria to increasing concentrations of penicillin in the laboratory. In both mutants the affinity of all four high molecular mass penicillin binding proteins (PBPs) for penicillin was drastically reduced accompanied by major changes in the composition of peptidoglycan as resolved by HPLC. The ratio of crosslinked to monomeric peptides became virtually inverted in the resistant cell walls with monomers representing two-thirds of the muropeptide species. The proportion of the crosslinked tri-tetra dimer, a major component of the cell wall of the original isolates, decreased to one-third or one-sixth of its normal representation, while the amounts of tripeptide monomers with an alanyl-serine substitution on the lysine epsilon amino group increased by close to a factor of two. The growth rates of both mutants decreased by a factor of approximately two, as compared to the original bacteria.
Insights
Penicillin resistance in Streptococcus pneumoniae significantly increased due to laboratory exposure. This resistance involved altered penicillin binding proteins (PBPs) and changes in bacterial cell wall structure, impacting growth rates.
Area of Science:
- Microbiology
- Biochemistry
- Molecular Biology
Background:
- Streptococcus pneumoniae is a major human pathogen.
- Antibiotic resistance is a growing global health concern.
- Understanding resistance mechanisms is crucial for developing new treatments.
Purpose of the Study:
- To investigate the mechanisms of penicillin resistance development in Streptococcus pneumoniae.
- To analyze changes in penicillin binding proteins (PBPs) and peptidoglycan structure associated with resistance.
Main Methods:
- Induction of penicillin resistance in clinical isolates of Streptococcus pneumoniae through laboratory exposure.
- Determination of minimum inhibitory concentrations (MICs) for penicillin.
- Analysis of high molecular mass penicillin binding proteins (PBPs) affinity for penicillin.
- High-performance liquid chromatography (HPLC) analysis of peptidoglycan composition.
Main Results:
- Penicillin MIC increased 100-fold and 20-fold in resistant mutants.
- Drastic reduction in penicillin affinity for all four high molecular mass PBPs observed.
- Major alterations in peptidoglycan composition, including inverted crosslinked to monomeric peptide ratio.
- Significant decrease in tri-tetra dimer and increase in specific tripeptide monomers in resistant cell walls.
- Growth rates of resistant mutants decreased by approximately 50%.
Conclusions:
- Gradual exposure to penicillin induces significant resistance in Streptococcus pneumoniae.
- Altered PBPs and modified peptidoglycan structure are key mechanisms of this resistance.
- Penicillin resistance is associated with a reduced growth rate in Streptococcus pneumoniae.