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Molecular epidemiology of sil locus in clinical Streptococcus pyogenes strains

Céline Plainvert1, Márcia Dinis2, Miriam Ravins3

  • 1Assistance Publique Hôpitaux de Paris, Service de Bactériologie, Centre National de Référence des Streptocoques, Groupe Hospitalier Paris Centre Cochin-Hôtel Dieu-Broca, Paris, France INSERM, U1016, Institut Cochin, Paris, France CNRS (UMR 8104), Paris, France Université Paris Descartes, Sorbonne Paris Cité, Paris, France.

Journal of Clinical Microbiology
|March 28, 2014
PubMed

Insights

The sil locus in Group A Streptococcus (GAS) is not linked to invasive disease. Most GAS strains lack a functional sil system, despite its presence in some emm genotypes.

Area of Science:

  • Microbiology
  • Bacterial Pathogenesis
  • Genetics

Background:

  • Streptococcus pyogenes (group A Streptococcus [GAS]) causes diverse infections, with regulatory mutations potentially driving invasiveness.
  • The sil locus, a quorum-sensing system, has been hypothesized to influence GAS invasiveness.
  • Previous studies suggested low sil prevalence and a link to genetic background, but invasiveness correlation was unassessed.

Purpose of the Study:

  • To investigate the prevalence of the sil locus in a large, diverse collection of GAS strains.
  • To determine the proportion of GAS strains with a functional sil system.
  • To assess the correlation between the sil locus and GAS invasiveness.

Main Methods:

  • Analysis of 637 nonredundant GAS strains from France with known clinical history and emm genotypes.
  • Detection of sil locus presence and prediction of functional sil system based on gene integrity.
  • Statistical assessment of the relationship between sil status and clinical presentation (invasive, noninvasive, carriage).

Main Results:

  • The sil locus was present in 206 out of 637 (32%) GAS strains, with prevalence varying significantly by emm genotype.
  • A functional sil system was predicted in only 9% of GAS strains due to inactivating mutations.
  • No correlation was found between the presence or absence of a functional sil locus and the invasiveness of the GAS strain.

Conclusions:

  • The sil locus prevalence in GAS is higher than previously reported but varies by emm genotype.
  • A functional sil system is rare in GAS strains, often due to inactivating mutations.
  • The sil locus, functional or not, does not appear to be a determinant of GAS invasiveness.

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