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Hemolytic mutants of group A Streptococcus pyogenes
Abstract:
Hemolytic mutants of Lancefield strain SS-95 and ATCC 19615 Streptococcus pyogenes were produced by treatment with N-methyl-N'-nitro-N-nitrosoguanidine. These mutants contained the same levels of streptolysin O, nicotinamide adenine dinucleotidase, deoxyribonuclease, and hyaluronidase. The mutants were deficient in streptolysin S, as was the naturally occurring nonhemolytic Lowry strain. The mutants retained their pathogenicity for mice and, when reisolated from the dead animals, produced the mutant hemolytic pattern.
Insights
Researchers created hemolytic mutants of Streptococcus pyogenes using chemical mutagens. These mutants, lacking streptolysin S but retaining other toxins, remained pathogenic in mice, demonstrating the importance of streptolysin S in S. pyogenes virulence.
Area of Science:
- Microbiology
- Molecular Biology
- Pathogenesis
Background:
- Streptococcus pyogenes is a significant human pathogen.
- Hemolytic activity is a key characteristic of virulent S. pyogenes strains.
- Streptolysin S (SLS) is a major cytotoxin implicated in S. pyogenes virulence.
Purpose of the Study:
- To generate and characterize hemolytic mutants of Streptococcus pyogenes.
- To investigate the role of streptolysin S in S. pyogenes pathogenicity.
- To assess the stability of the induced hemolytic phenotype.
Main Methods:
- Chemical mutagenesis of S. pyogenes strains (Lancefield SS-95, ATCC 19615) using N-methyl-N'-nitro-N-nitrosoguanidine.
- Quantification of extracellular toxins: streptolysin O (SLO), nicotinamide adenine dinucleotidase (NADase), deoxyribonuclease (DNase), and hyaluronidase.
- Assessment of hemolytic activity and determination of streptolysin S (SLS) deficiency.
- Pathogenicity testing in a mouse model.
- Reisolation and characterization of S. pyogenes from infected animals.
Main Results:
- Hemolytic mutants were successfully generated.
- Mutants exhibited deficiency in streptolysin S (SLS), similar to the naturally nonhemolytic Lowry strain.
- Levels of streptolysin O (SLO), NADase, DNase, and hyaluronidase remained comparable to wild-type strains.
- Mutants retained pathogenicity in mice.
- Reisolated mutants from infected mice exhibited the same hemolytic deficiency.
Conclusions:
- Streptolysin S (SLS) is essential for the characteristic hemolytic activity of Streptococcus pyogenes.
- Deficiency in SLS does not abolish the pathogenicity of S. pyogenes in a mouse model.
- The generated mutants provide valuable tools for studying S. pyogenes virulence factors.
- The hemolytic phenotype of the induced mutants is stable and heritable.