title: Clinical and microbiological characterization of serotype 6D pneumococcal infections in South Korea.
abstract: BACKGROUND
  The prevalence of Serotype 6D Streptococcus pneumoniae was reported relatively high in South Korea. Since the introduction of 7-valent pneumococcal conjugate vaccine (PCV7), serotype replacement was observed. This study was designed to better clarify genetic diversity of pneumococcal serotype 6D and its clinical characteristics after introduction of PCV7 in 2000.
  
  
  METHODS
  We performed serotyping analysis with 1298 pneumococcal isolates from clinical specimens in South Korea from 2004 to 2011. Multilocus sequence typing was performed, and minimal inhibitory concentration was determined for the available serotype 6D and nontypeable (NT) pneumococcal isolates during the 2006-2007 period.
  
  
  RESULTS
  The proportion of serotype 6D pneumococci increased from 0.8% (2004-2007) to 2.9% (2008-2011) of all clinical pneumococcal isolates, accounting for 14.9% of serogroup 6 pneumococci in South Korea. NT pneumococci markedly increased to 13.3% during 2006-2007 in advance of the increase in serotype 6D. Among the 26 available serotype 6D pneumococcal isolates, ST282 was predominant (23 isolates, 88.5%). The STs of NT pneumococci (26 isolates) were diverse, but clonal complex 271 was the dominant clone. The oral penicillin non-susceptibility rate was 92.3% (24 among 26 isolates) for both serotype 6D and NT pneumococci. The ceftriaxone non-susceptibility rates of serotype 6D and NT pneumococci were 7.7% and 3.8%, respectively.
  
  
  CONCLUSIONS
  ST228(6D) strain expanded, particularly among old adults with comorbidities in South Korea. Both antibiotic and PCV7 pressure might have contributed to the selective increase of NT and serotype 6D pneumococci.
authors.affiliation: Department of Internal Medicine, Korea University Guro Hospital, Korea University College of Medicine, Seoul, Republic of Korea.
authors.forename: Hee Jin
authors.initials: HJ
authors.lastname: Cheong
authors.affiliation: Department of Internal Medicine, Korea University Guro Hospital, Korea University College of Medicine, Seoul, Republic of Korea. Electronic address: infection@korea.ac.kr.
authors.forename: Joon Young
authors.initials: JY
authors.lastname: Song
authors.affiliation: Department of Internal Medicine, Korea University Guro Hospital, Korea University College of Medicine, Seoul, Republic of Korea.
authors.forename: Min Joo
authors.initials: MJ
authors.lastname: Choi
authors.affiliation: Department of Internal Medicine, Korea University Guro Hospital, Korea University College of Medicine, Seoul, Republic of Korea.
authors.forename: Ji Ho
authors.initials: JH
authors.lastname: Jeon
authors.affiliation: Department of Internal Medicine, Korea University Guro Hospital, Korea University College of Medicine, Seoul, Republic of Korea.
authors.forename: Seong Hee
authors.initials: SH
authors.lastname: Kang
authors.affiliation: Department of Internal Medicine, Korea University Guro Hospital, Korea University College of Medicine, Seoul, Republic of Korea.
authors.forename: Eun Joo
authors.initials: EJ
authors.lastname: Jeong
authors.affiliation: Department of Internal Medicine, Korea University Guro Hospital, Korea University College of Medicine, Seoul, Republic of Korea.
authors.forename: Ji Yun
authors.initials: JY
authors.lastname: Noh
authors.affiliation: Department of Internal Medicine, Korea University Guro Hospital, Korea University College of Medicine, Seoul, Republic of Korea.
authors.forename: Woo Joo
authors.initials: WJ
authors.lastname: Kim
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000900:Anti-Bacterial Agents / Q000627:therapeutic use; D002443:Ceftriaxone / Q000627:therapeutic use; D002648:Child; D002675:Child, Preschool; D005260:Female; D014644:Genetic Variation / Q000235:genetics; D006801:Humans; D008297:Male; D008826:Microbial Sensitivity Tests / Q000379:methods; D008875:Middle Aged; D058885:Multilocus Sequence Typing / Q000379:methods; D011008:Pneumococcal Infections / Q000188:drug therapy / Q000453:epidemiology / Q000276:immunology / Q000382:microbiology*; D022242:Pneumococcal Vaccines / Q000276:immunology; D056910:Republic of Korea / Q000453:epidemiology; D065288:Serogroup; D012703:Serotyping / Q000379:methods; D013296:Streptococcus pneumoniae / Q000187:drug effects / Q000235:genetics* / Q000276:immunology / Q000302:isolation & purification*; D018074:Vaccines, Conjugate / Q000276:immunology; D055815:Young Adult
chemical_list: D000900:Anti-Bacterial Agents; D022242:Pneumococcal Vaccines; D018074:Vaccines, Conjugate; D002443:Ceftriaxone
keywords: Capsular serotype; Multilocus sequence typing; Serotyping; Streptococcus pneumoniae