Genetic Diversity of the Pneumococcal Capsule: Implications for Molecular-based Serotyping

Mary Catherine McEllistrem


Future Microbiol. 2009;4(7):857-865. 

In This Article

Capsular Locus

The capsular locus has been fully sequenced for 91 pneumococcal serotypes, and is between 10 and 30 kb in length. Among the 91 serotypes, the alternative coding DNA of the capsular operon exceeds 1.8 Mbp.[11] All of the capsular operons are flanked by the conserved dexB and aliA genes.[11,12] For serotype 37, the capsular locus consists of mutated serotype 33F genes; the serotype 37 capsule is synthesized by the tts gene, which is located far apart from the capsular locus.[13] All except serotypes 3 and 37 use the regulatory and processing genes wzg, wzh, wzd and wze (also known as cpsA–D, respectively), and synthesize capsule via the Wzx/Wzy-dependent pathway. The wzx gene encodes a polysaccharide transporter or flippase, while the wzy gene encodes a polysaccharide polymerase. By contrast, serotypes 3 and 37 use a synthase pathway.[14,15]


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