Background: In this study, we defined the population biology of serogroup 6 Streptococcus pneumoniae collected\nin China and their antibiotic resistance profiles.\nMethods: The serotypes of 225 S. pneumoniae strains isolated between 1997 and 2011 were identified with the\nQuellung reaction and serotype-specific PCR. All isolated pneumococci were tested for their sensitivity to 11 kinds\nof antibiotics with the E-test method or disc diffusion. The sequence types (STs) were analyzed with multilocus\nsequence typing (MLST).\nResults: The frequencies of serotypes and subtypes 6A, 6B-I, 6B-II, 6C, and 6D among the 225 isolates were 46.7%\n(105/225), 19.6% (44/225), 25.8% (58/225), 6.2% (14/225), and 1.8% (4/225), respectively. Serotype 6E was not found\nin the serotype 6A isolates, and neither serotype 6F nor 6G was identified in any isolate. MLST analysis revealed\n58 STs. The most common STs were ST982 (23.1%), ST90 (14.7%), ST4542 (7.6%), and ST2912 (4.9%). The rates of clonal\ncomplex 90 (CC90) and CC386 among the oral-penicillin-nonsusceptible isolates decreased over the years, whereas the\nrates of CC855 and CC3173 increased. The four CCs had similar penicillin MIC distributions, with a maximum MIC of\n2 ?g/ml.\nConclusions: This study identified the serotypes/subtypes and CCs/STs of group 6 S. pneumoniae present in China. No\nsalient antibiotic-resistant clones were isolated among the serogroup 6 S. pneumoniae.
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