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

Streptococcus pneumoniae, the aetiological agent of pneumonia and non-gonococcal urethritis, shares a high degree of DNA sequence identity with the viridans group of streptococci, particularlyStreptococcus mitisandStreptococcus oralis. Although their clinical and pathological manifestations are different, discrimination betweenS. pneumoniaeand its close viridans cocci relatives is still quite difficult. Suppression subtractive hybridization was performed to identify the genomic differences betweenS. pneumoniaeandS. mitis. Thirty-four resultingS. pneumoniae-specific clones were examined by sequence determination and comparative DNA sequence analysis usingblast.S. pneumoniae-specific primers were subsequently designed from one of the clonal DNA sequences containing thecpsgene (coding for capsular polysaccharide biosynthesis). The primer specificities were evaluated using 49 viridans streptococci including 26S. pneumoniae, 54 other streptococci, 14Lactococcusspecies, 14Enterococcusspecies and threeVagococcusspecies, and compared with the specificities of previously described autolysin (lytA), pneumolysin (ply), Spn9802 and Spn9828 primers. The newly designedcpsA-specific primer set was highly specific toS. pneumoniaeand was even better than the existing primers. These findings may help improve the rapid identification and differentiation ofS. pneumoniaefrom closely related members of the viridans group streptococci.