Assessment of multidrug resistance, clonality and virulence in non-PCV-13 Streptococcus pneumoniae serotypes in Canada, 2011-13

J Antimicrob Chemother. 2015 Jul;70(7):1960-4. doi: 10.1093/jac/dkv061. Epub 2015 Mar 11.


Objectives: Serotype replacement in Streptococcus pneumoniae following the implementation of a new vaccine has been associated with the emergence of non-vaccine serotypes as prominent causes of invasive pneumococcal disease (IPD). The aim of this study was to characterize specific non-PCV-13 serotypes 15A, 22F, 33F and 35B from IPD, isolated in Canada post-PCV-13 introduction in 2010.

Methods: Of 3802 IPD isolates collected from across Canada in 2011-13, 18.4% were found to be serotypes 15A, 22F, 33F and 35B. These 699 isolates were subjected to antimicrobial susceptibility testing, PFGE, MLST, molecular detection of pneumococcal pili and comparison with Pneumococcal Molecular Epidemiology Network (PMEN) clones.

Results: This study demonstrated clonal spread of specific STs, including MDR ST63 and its Sweden(15A)-25-related variants, the increasingly common ST433 and a variant of piliated, penicillin-non-susceptible ST558, related to PMEN clone Utah(35B)-24 (ST377). New STs of serotype 33F were identified. Several potential capsular switching events were identified within these serotypes.

Conclusions: Non-PCV-13 serotype 22F is increasing in Canada through the rapid clonal expansion of ST433. Numerous new STs associated with serotype 33F indicate the potential divergence of the serotype. Serotypes 15A and 35B in Canada are related to international clones of S. pneumoniae.

Keywords: MLST; S. pneumoniae; antimicrobial drug resistance; multilocus sequence typing; non-PCV-13 serotypes.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Canada / epidemiology
  • Drug Resistance, Multiple, Bacterial*
  • Fimbriae Proteins / genetics
  • Genotype*
  • Humans
  • Microbial Sensitivity Tests
  • Molecular Typing
  • Pneumococcal Infections / epidemiology
  • Pneumococcal Infections / microbiology*
  • Pneumococcal Vaccines / immunology
  • Prevalence
  • Serogroup*
  • Streptococcus pneumoniae / classification*
  • Streptococcus pneumoniae / drug effects*
  • Streptococcus pneumoniae / isolation & purification
  • Virulence
  • Virulence Factors / genetics*


  • 13-valent pneumococcal vaccine
  • Pneumococcal Vaccines
  • Virulence Factors
  • Fimbriae Proteins