Biochemical, genetic, and serological characterization of two capsule subtypes among Streptococcus pneumoniae Serotype 20 strains: discovery of a new pneumococcal serotype.

ABSTRACT: The bacterial pathogen Streptococcus pneumoniae expresses one of over 90 structurally distinct polysaccharide (PS) capsule serotypes. Prior PS structural analyses of the vaccine-associated serotype 20 do not agree with reports describing the genes that mediate capsule synthesis. Furthermore, using immunized human sera-based assays, serological differences were recently noted among strains typed as serotype 20. We examined the capsule structures of two serologically dissimilar serotype 20 strains, 20? and 20?, by extensive biochemical analysis. 20? PS was composed of the previously described serotype 20 hexasaccharide repeat unit, whereas the 20? PS was composed of a novel heptasaccharide repeat unit containing an extra branching ?-glucose residue. Genetic analysis of the subtypes revealed that 20? may have arisen from a 20? progenitor following loss of function mutation to the glycosyltransferase gene whaF. Conventional serotyping methods using rabbit polyclonal or mouse monoclonal antibodies were unable to distinguish the subtypes. However, genetic analysis of multiple "serotype 20" clinical isolates revealed that all strains contain the 20? genotype. We propose naming bacteria that express the previously described 20? capsule structure 20A and bacteria that express the novel 20? capsule structure 20B, a new pneumococcal serotype.

SUBMITTER: Calix JJ 

PROVIDER: S-EPMC3431705 | biostudies-literature | 2012 Aug

REPOSITORIES: biostudies-literature