We investigated the genetic structure of Streptococcus pneumoniae isolated from Korean children prior to the use of heptavalent pneumococcal conjugate vaccine (PCV7). A total of 278 pneumococcal isolates were obtained from invasive (n = 77) and noninvasive (n = 201) specimens from children < 5 years of age that visited the Seoul National University Children's Hospital between 1995 and 2005; these samples were serotyped. Two hundred seventy-eight isolates were characterized by multilocus sequence typing, antibiotic susceptibility pattern testing with the E-test. The common serotypes were 19F (22.7%), 23F (19.1%), 19A (14.4%), 6B (11.2%), 6A (8.3%), 14 (5.4%), and 9V (4.3%); these 7 serotypes accounted for 85.3% of the 278 isolates. The isolates belonged to 23 serotypes and 81 sequence types (STs) (including 48 newly discovered STs). The eBURST analysis showed 7 clonal complexes (CCs). CC271 was the main CC of serogroup 19; CC81 and CC3115, serotype 6A; CC81 and CC880, serotype 23F; CC90, serotype 6B; CC166, serotype 9V; and CC554, serotype 14. Nonsusceptibility rates to penicillin and erythromycin among the invasive isolates were 9.1% and 94.8%, respectively. The resultant database may be useful for postvaccine surveillance.
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