Capsular Sequence Typing – Typing Tool Introduction

The CST is a molecular method to genotype the capsular locus in order to assess the serotype. CST is based on a part of the sequence of the wzh gene. This gene was chosen for sequencing because it varies sufficiently between serotypes, but is conserved enough to amplify the same gene segment of the various serotypes using a single mix of primers. The primers used in the CST are based on the publicly available sequences of the capsular genes of the 90 pneumococcal serotypes described by Bentley et al. (2006 PLoS Genet 2:e31.). After sequencing of 506 base pairs of the wzh gene, a capsular type (CT) can be assigned. The CT is a composite assignment; the first part of the assignment is based on the phenotype assessed by conventional serotyping and the second part of the assignment is the consecutive number of the capsular type belonging to the same serotype. As an example, CT09V-01 designated the first variant in wzh sequence of an isolate serotyped as 9V.