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Factors affecting sensitivity of group B streptococci to an exogenous murein hydrolase
Abstract:
Group B streptococci treated with cell wall synthesis inhibitors (penicillin or vancomycin) or by a variety of membrane-acting agents are sensitized to the lytic action of exogenous M1 muramidase. Muramidase without a sensitizing agent caused rupture of bacterial chains only, accompanied by the release of a small amount of cell wall peptidoglycan label and an increase of the number of colony-forming units. In combination with sensitizing agents the exogenous muramidase appeared to initiate hydrolysis of biosynthetically new peptidoglycan. Treatment of the cells with chloramphenicol or starvation for nutritionally required amino acids suppressed the rate of cell lysis and peptidoglycan hydrolysis during subsequent sensitization and muramidase treatment of the bacteria. Purified cell walls prepared from the amino acid starved cells were also hydrolyzed with a slower rate by muramidase. It is suggested that agents sensitizing the bacteria to the exogenous muramidase act by perturbing or removing some nonmurein components of the cell envelope which protect the peptidoglycan from the activity of exogenous enzyme. Agents increasing resistance against exogenous muramidase may also cause some alteration in peptidoglycan structure.
Insights
Group B streptococci treated with cell wall inhibitors become sensitive to muramidase. This enzyme then degrades newly synthesized peptidoglycan, suggesting cell wall protection is compromised.
Area of Science:
- Microbiology
- Bacterial Cell Wall Biology
- Enzymology
Background:
- Group B Streptococcus (GBS) is a significant human pathogen.
- Bacterial cell wall integrity is crucial for survival.
- Muramidases are enzymes that degrade peptidoglycan, a key cell wall component.
Purpose of the Study:
- To investigate the sensitization of GBS to exogenous M1 muramidase.
- To understand the mechanism by which cell wall synthesis inhibitors and membrane-acting agents affect bacterial susceptibility to lysis.
- To explore the role of peptidoglycan synthesis and cell envelope components in muramidase activity.
Main Methods:
- Treatment of GBS with penicillin, vancomycin, and membrane-acting agents.
- Exposure of treated bacteria to exogenous M1 muramidase.
- Analysis of bacterial lysis, peptidoglycan hydrolysis, and colony-forming units.
- Investigation of the effects of chloramphenicol treatment and amino acid starvation on muramidase activity.
- Hydrolysis of purified cell walls from starved bacteria.
Main Results:
- Cell wall synthesis inhibitors and membrane agents sensitized GBS to M1 muramidase.
- Muramidase alone caused limited lysis and peptidoglycan release.
- In combination with sensitizing agents, muramidase initiated hydrolysis of newly synthesized peptidoglycan.
- Chloramphenicol treatment or amino acid starvation reduced lysis and peptidoglycan hydrolysis rates.
- Purified cell walls from starved cells showed slower hydrolysis by muramidase.
Conclusions:
- Sensitizing agents likely perturb or remove protective non-murein cell envelope components.
- These altered components expose peptidoglycan to exogenous muramidase activity.
- Agents conferring resistance may alter peptidoglycan structure, affecting enzyme accessibility.