Clonal and serotype dynamics of serogroup 6 isolates causing invasive pneumococcal disease in Portugal: 1999-2012

PLoS One. 2017 Feb 2;12(2):e0170354. doi: 10.1371/journal.pone.0170354. eCollection 2017.


Although serogroup 6 was among the first to be recognized among Streptococcus pneumoniae, several new serotypes were identified since the introduction of pneumococcal conjugate vaccines (PCVs). A decrease of the 6B-2 variant among invasive pneumococcal disease (IPD), but not 6B-1, was noted post conjugate vaccine introduction, underpinned by a decrease of CC273 isolates. Serotype 6C was associated with adult IPD and increased in this age group representing two lineages (CC315 and CC395), while the same lineages expressed other serogroup 6 serotypes in children. Taken together, these findings suggest a potential cross-protection of PCVs against serotype 6C IPD among vaccinated children but not among adults. Serotype 6A became the most important serogroup 6 serotype in children but it decreased in adult IPD. No other serogroup 6 serotypes were detected, so available phenotypic or simple genotypic assays remain adequate for distinguishing serotypes within serogroup 6 isolates.

MeSH terms

  • Adult
  • Anti-Bacterial Agents / pharmacology
  • Cross Protection / immunology*
  • Heptavalent Pneumococcal Conjugate Vaccine / immunology*
  • Humans
  • Immunologic Deficiency Syndromes / epidemiology*
  • Immunologic Deficiency Syndromes / microbiology
  • Interleukin-1 Receptor-Associated Kinases
  • Microbial Sensitivity Tests
  • Multilocus Sequence Typing
  • Pneumococcal Infections / epidemiology*
  • Pneumococcal Infections / microbiology
  • Pneumococcal Vaccines / immunology*
  • Portugal / epidemiology
  • Primary Immunodeficiency Diseases
  • Serogroup
  • Streptococcus pneumoniae / classification
  • Streptococcus pneumoniae / genetics*
  • Streptococcus pneumoniae / immunology*
  • Streptococcus pneumoniae / isolation & purification
  • Vaccination


  • 10-valent pneumococcal conjugate vaccine
  • 13-valent pneumococcal vaccine
  • Anti-Bacterial Agents
  • Heptavalent Pneumococcal Conjugate Vaccine
  • Pneumococcal Vaccines
  • Interleukin-1 Receptor-Associated Kinases

Supplementary concepts

  • IRAK4 Deficiency
  • Invasive Pneumococcal Disease, Recurrent Isolated, 2

Grant support

J. Diamantino-Miranda and S.I. Aguiar were supported by grants SFRH/BD/81766/2011 and SFRH/BPD/78376/2011, respectively, from Fundação para a Ciência e Tecnologia, Portugal. The work was partly supported by Fundação para a Ciência e Tecnologia, Portugal (PTDC/DTP-EPI/1759/2012 and PTDC/DTP-EPI/1555/2014) and an unrestricted Investigator initiated project from Pfizer. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.