Identification of the cpsA gene as a specific marker for the discrimination of Streptococcus pneumoniae from viridans group streptococci

<jats:p><jats:italic>Streptococcus pneumoniae</jats:italic>, the aetiological agent of pneumonia and non-gonococcal urethritis, shares a high degree of DNA sequence identity with the viridans group of streptococci, particularly<jats:italic>Streptococcus mitis</jats:italic>and<jats:italic>Streptococcus oralis</jats:italic>. Although their clinical and pathological manifestations are different, discrimination between<jats:italic>S. pneumoniae</jats:italic>and its close viridans cocci relatives is still quite difficult. Suppression subtractive hybridization was performed to identify the genomic differences between<jats:italic>S. pneumoniae</jats:italic>and<jats:italic>S. mitis</jats:italic>. Thirty-four resulting<jats:italic>S. pneumoniae</jats:italic>-specific clones were examined by sequence determination and comparative DNA sequence analysis using<jats:sc>blast</jats:sc>.<jats:italic>S. pneumoniae</jats:italic>-specific primers were subsequently designed from one of the clonal DNA sequences containing the<jats:italic>cps</jats:italic>gene (coding for capsular polysaccharide biosynthesis). The primer specificities were evaluated using 49 viridans streptococci including 26<jats:italic>S. pneumoniae</jats:italic>, 54 other streptococci, 14<jats:italic>Lactococcus</jats:italic>species, 14<jats:italic>Enterococcus</jats:italic>species and three<jats:italic>Vagococcus</jats:italic>species, and compared with the specificities of previously described autolysin (<jats:italic>lytA</jats:italic>), pneumolysin (<jats:italic>ply</jats:italic>), Spn9802 and Spn9828 primers. The newly designed<jats:italic>cpsA</jats:italic>-specific primer set was highly specific to<jats:italic>S. pneumoniae</jats:italic>and was even better than the existing primers. These findings may help improve the rapid identification and differentiation of<jats:italic>S. pneumoniae</jats:italic>from closely related members of the viridans group streptococci.</jats:p>