title: Diversity and antibiotic resistance among nonvaccine serotypes of Streptococcus pneumoniae carriage isolates in the post-heptavalent conjugate vaccine era.
abstract: BACKGROUND
  In response to the selective pressure of pneumococcal conjugate vaccine, increased asymptomatic carriage of antibiotic-nonsusceptible nonvaccine serotypes (NVTs) has been observed. Possible mechanisms include de novo acquisition of resistance, serotype switching, introduction of new clones, and expansion of existing clones.
  
  
  METHODS
  To investigate the process of increased antibiotic nonsusceptibility among replacing serotypes, we applied multilocus sequence typing to samples of 126 and 222 pneumococci collected in 2001 and 2004, respectively, from the nasopharynges of children <7 years of age in 16 Massachusetts communities.
  
  
  RESULTS
  We found no evidence of penicillin resistance due to either serotype switching or de novo acquisition. Nonetheless, resistance increased through the expansion of previously recognized clones of NVTs, particularly in serotypes 19A, 15A, and 35B. In 19A, several unrelated clones increased in frequency, whereas, in the other 2 serotypes, single resistant lineages were responsible for the increased prevalence of resistant strains.
  
  
  CONCLUSIONS
  The decreased prevalence of antibiotic resistance with the introduction of heptavalent pneumococcal conjugate vaccine is likely to be partially eroded over time as vaccine-included serotypes are replaced by resistant clones of NVTs. The clinical significance of this will depend on the pathogenic potential of replacing clones to cause local (e.g., otitis media) or invasive disease.
authors.affiliation: Department of Infectious Disease Epidemiology, Imperial College, London, UK. w.hanage@imperial.ac.uk
authors.forename: William P
authors.initials: WP
authors.lastname: Hanage
authors.forename: Susan S
authors.initials: SS
authors.lastname: Huang
authors.forename: Marc
authors.initials: M
authors.lastname: Lipsitch
authors.forename: Cynthia J
authors.initials: CJ
authors.lastname: Bishop
authors.forename: Daniel
authors.initials: D
authors.lastname: Godoy
authors.forename: Stephen I
authors.initials: SI
authors.lastname: Pelton
authors.forename: Richard
authors.initials: R
authors.lastname: Goldstein
authors.forename: Heather
authors.initials: H
authors.lastname: Huot
authors.forename: Jonathan A
authors.initials: JA
authors.lastname: Finkelstein
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002353:Carrier State / Q000453:epidemiology* / Q000382:microbiology; D002648:Child; D002675:Child, Preschool; D004351:Drug Resistance; D000069443:Heptavalent Pneumococcal Conjugate Vaccine; D006801:Humans; D008404:Massachusetts / Q000453:epidemiology; D022401:Meningococcal Vaccines; D009305:Nasopharynx / Q000382:microbiology; D011008:Pneumococcal Infections / Q000382:microbiology / Q000517:prevention & control*; D022242:Pneumococcal Vaccines; D018571:Sentinel Surveillance; D012703:Serotyping; D013296:Streptococcus pneumoniae / Q000145:classification* / Q000187:drug effects*; D013997:Time Factors; D014611:Vaccination; D018074:Vaccines, Conjugate
chemical_list: D000900:Anti-Bacterial Agents; D000069443:Heptavalent Pneumococcal Conjugate Vaccine; D022401:Meningococcal Vaccines; D022242:Pneumococcal Vaccines; D018074:Vaccines, Conjugate