Genetic structure of Streptococcus pneumoniae isolated from children in a tertiary care university hospital, in Korea, 1995 to 2005

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.