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Multilocus sequence typing of serotype III group B streptococcus and correlation with pathogenic potential

H Dele Davies1, Nicola Jones, Thomas S Whittam

  • 1Department of Microbiology, and Child Health Research Unit, Alberta Children's Hospital, University of Calgary, Canada. daviesde@msu.edu

The Journal of Infectious Diseases
|March 5, 2004
PubMed

Insights

Serotype III group B streptococcus (GBS) clones ST-19 and ST-17 are common in invasive and colonizing infections. These major GBS clones were not linked to increased infant disease or lower maternal antibodies, suggesting other factors may be involved.

Area of Science:

  • Microbiology
  • Genetics
  • Infectious Diseases

Background:

  • Serotype III group B streptococcus (GBS) is a leading cause of invasive infant disease in North America.
  • Understanding the genetic diversity and clonal structure of GBS is crucial for developing effective prevention and treatment strategies.

Purpose of the Study:

  • To identify and characterize clones within invasive and colonizing serotype III GBS isolates.
  • To investigate the association between specific GBS clones, invasive disease, and maternal antibody levels.

Main Methods:

  • Multilocus sequence typing (MLST) was employed to analyze 28 invasive and 55 colonizing serotype III GBS isolates.
  • Allelic profiles were concatenated and grouped to understand clonal relationships.
  • Statistical analysis was used to assess the association between sequence types (STs), invasive disease, and maternal immunoglobulin G (IgG) levels.

Main Results:

  • Ten allelic sequence types (STs) were identified, with ST-19 and ST-17 being the predominant profiles in both invasive (57.1% and 32.1%) and colonizing (58.2% and 29.1%) isolates, respectively.
  • The STs converged into three main groups, with Group 1 (ST-19 complex) showing close relation to a serotype V reference genome, suggesting potential capsule switching.
  • No significant association was found between the major sequence types (ST-19 and ST-17) and increased invasiveness or lower maternal capsular polysaccharide-specific IgG levels.

Conclusions:

  • Dominant clones of serotype III GBS, specifically ST-19 and ST-17, are prevalent in both invasive and colonizing infections.
  • The findings do not support a direct link between these major clones and increased infant disease severity or reduced maternal antibody protection.
  • The genetic relatedness of ST-19 to a serotype V strain suggests horizontal gene transfer and capsule switching as a potential evolutionary mechanism in GBS.

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