Recently, @entity328 serotypes 6C and 6D have been identified. It is thought that they emerged by the replacement of wciN(b) in the capsular loci of serotypes 6A and 6B, respectively. However, their evolution has not been unveiled yet. To investigate the evolution of four serotypes of @entity2260 serogroup 6, four genes of the @entity9998 ( @entity9998 ) locus, wchA, wciN, wciO, and wciP, of isolates of @entity2260 serotypes 6A, 6B, 6C, and 6D were sequenced. Multilocus sequence typing (MLST) was performed to investigate their genetic backgrounds. The wchA gene of serotype 6C and 6D isolates was distinct from that of serotype 6A and 6B isolates, which may suggest cotransfer of wchA with wciN(b). Otherwise, serotypes 6C and 6D displayed different genetic backgrounds from serotypes 6A and 6B, which was suggested by MLST analysis. In addition, serotype 6C isolates showed distinct wciP polymorphisms from other serotypes, which also indicated that serotype 6C had not recently originated from serotype 6A. Although serotype 6D shared the same @entity535 polymorphisms of wciO with serotype 6B, wciP of serotype 6D differed from that of serotype 6B. The data indicate the implausibility of the scenario of a recent emergence of the @entity9998 locus of serotype 6D by genetic recombination between serotypes 6B and 6C. In addition, five serotype 6A and 6B isolates (6X group) displayed @entity9998 loci distinct from those of other isolates. The @entity9998 locus homogeneity and similar sequence types in MLST analysis suggest that most of the 6X group of isolates originated from the same ancestor and that the entire @entity9998 locus might have recently been transferred from an unknown origin. Serotype 6B isolates showed two or more @entity9998 locus subtypes, indicating a recombination-mediated mosaic structure of the @entity9998 locus of serotype 6B. The collective data favor the emergence of @entity9998 loci of serotypes 6A, 6B, 6C, and 6D by complicated recombination.

Comparison of capsular genes of XXXX serotype 6A, 6B, 6C, and 6D isolates.

@entity535 :: ('CHEBI:33704', 'Chemical') :: ['amino acid'] @entity9998 :: ('MESH:D017889', 'Disease') :: ['cps', 'capsular polysaccharide synthesis'] @entity2260 :: ('2104', 'Species') :: ['S. pneumoniae'] @entity328 :: ('1313', 'Species') :: ['Streptococcus pneumoniae']
@entity328 :: (1313,Species) :: ['Streptococcus pneumoniae']
