Background: Two atypical serogroup 6 strains have been discovered. Results: They express capsular polysaccharide with two different repeating units and share A150T mutation in WciN␣. Conclusion: This mutation shifts WciN␣ from a galactosyltransferase to a bi-specific glycosyltransferase, creating two new hybrid serotypes: 6F and 6G. Significance: Pneumococci can change capsule serotypes by point mutations and may alter their interactions with the immunity of the host.

This study presents serogroup 6 isolates from invasive pneumococcal disease (IPD) before and after the recommendation for childhood pneumococcal conjugate vaccination in Germany (July 2006). A total of 19,299 (children: 3508, adults: 15,791) isolates were serotyped. Serogroup 6 isolates accounted for 9.5% (children) and 6.7% (adults), respectively. 548 isolates had serotype 6A, 558 had serotype 6B, 285 had serotype 6C, and 4 had serotype 6D. Among children, serotype 6B was most prevalent (7.5% of isolates) before vaccination, followed by 6A and 6C. After the 7-valent pneumococcal conjugate vaccine (PCV7), the prevalence of serotype 6B significantly decreased (p = 0.040), a pattern which continued in the higher-valent PCV period (PCV10, PCV13). Serotype 6A prevalence showed a slight increase directly after the start of PCV7 vaccination, followed by a decrease which continued throughout the PCV10/13 period. Serotype 6C prevalence remained low. Serotype 6D was not found among IPD isolates from children. Among adults, prevalence of both 6A and 6B decreased, with 6B reaching statistical significance (p = 0.045) and 6A showing a small increase in 2011–2012. Serotype 6C prevalence was 1.5% or lower before vaccination, but increased post-vaccination to 3.6% in 2011/12 (p = 0.031). Four serotype 6D isolates were found post-PCV7 childhood vaccination, and two post-PCV10/13. Antibiotic resistance was found mainly in serotype 6B; serotype 6A showed lower resistance rates. Serotype 6C isolates only showed resistance among adults; serotype 6D isolates showed no resistance. Multilocus sequence typing showed that sequence type (ST) 1692 was the most prevalent serotype 6C clone. Thirty-two other STs were found among serotype 6C isolates, of which 12 have not been previously reported. The four serotype 6D isolates had ST 948, ST 2185 and two new STs: 8422 and 8442. Two serogroup 6 isolates could not be assigned to a serotype, but had STs common to serogroup 6.

PAGE 25978:The legend for Fig. 2 should be revised as follows. FIGURE 2. 6X11 and 6X12 are serologically distinct from other members in serogroup 6. Flow cytometry histograms of various pneumococcal strains (indicated at the left of each row) that were stained with different mAbs (indicated at the bottom of each column) are shown. The shaded area in each panel represents non-specific staining by the secondary antibodies and was obtained by simultaneously staining TIGR6A with both anti-IgG and anti-IgM antibodies in the absence of monoclonal antibodies. In unpublished experiments, all isogenic serogroup 6 strains had low staining by secondary antibodies (mean fluorescence index Ͻ5).

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