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Molecular subtyping of prevalent M serotypes of Streptococcus pyogenes causing invasive disease
1Molecular Biology Unit, Central Public Health Laboratory, London, United Kingdom.
Abstract:
Reproducible methodologies and a scheme for high-resolution genotyping of Streptococcus pyogenes were defined with respect to a study of six predominant M serotypes causing invasive group A streptococcal disease in the United Kingdom. Serotype reference strains were compared with nine clinical isolates of each serotype from patients with diseases such as pneumonia, puerperal sepsis, toxic shock-like-syndrome, cellulitis, or necrotizing fasciitis. Four enzymes were evaluated for their discriminatory power in 16S rRNA gene-specific ribotyping. Discriminatory power was greatest with EcoRI, which generated serotype-specific ribotypes, and with SacI, which could subdivide strains of the same M serotype. Twenty-five combined ribotypes were found among the 60 strains, and the indices of discriminatory power (D values) of this method varied from 0.51 within serotype M1 to 0.98 within strains of serotype M5. Macrorestriction with the rarely cutting endonuclease SmaI and pulsed-field gel electrophoresis gave D values varying from 0.37 within serotype M1 to the maximal 1.0 within serotype M5. Comparison of macrorestriction profiles revealed various degrees of genetic heterogeneity within M serotypes. Strains of M1, M3, M6, and M11 exhibited clonally related macrorestriction profiles, while those of R28 and M5 strains were consistent with polyphyletic origin.
Insights
High-resolution genotyping of Streptococcus pyogenes using ribotyping and macrorestriction revealed genetic diversity within M serotypes. These methods are crucial for understanding invasive group A streptococcal disease outbreaks.
Area of Science:
- Microbiology
- Genetics
- Epidemiology
Background:
- Streptococcus pyogenes (group A Streptococcus) causes invasive diseases.
- Understanding the genetic diversity of S. pyogenes is essential for tracking disease outbreaks.
Purpose of the Study:
- To define reproducible methods for high-resolution genotyping of S. pyogenes.
- To assess genetic heterogeneity within six predominant M serotypes causing invasive disease.
Main Methods:
- Evaluated 16S rRNA gene-specific ribotyping with four enzymes (EcoRI, SacI).
- Utilized macrorestriction with SmaI and pulsed-field gel electrophoresis.
- Compared reference strains with 60 clinical isolates from invasive disease patients.
Main Results:
- EcoRI generated serotype-specific ribotypes; SacI subdivided strains within M serotypes.
- Twenty-five combined ribotypes were identified among 60 strains.
- Macrorestriction and pulsed-field gel electrophoresis revealed genetic heterogeneity; some serotypes showed clonal relatedness, others polyphyletic origin.
Conclusions:
- Established reproducible high-resolution genotyping methods for S. pyogenes.
- Demonstrated significant genetic diversity within M serotypes of S. pyogenes.
- These genotyping techniques are valuable for studying invasive group A streptococcal disease.