Additive attenuation of virulence of Streptococcus pneumoniae by mutation of the genes encoding pneumolysin and other putative pneumococcal virulenceproteins

Although the polysaccharide capsule of Streptococcus pneumoniae has been re cognized as a sine qua non of virulence, much recent attention has focused on the role of pneumococcal proteins in pathogenesis, particularly in view of their potential as vaccine antigens. The individual contributions of pne umolysin (Ply), the major neuraminidase (NanA), autolysin (LytA), hyaluroni dase (Hyl), pneumococcal surface protein A (PspA), and choline-binding prot ein A (CbpA) have been examined by specifically mutagenizing the respective genes in the pneumococcal chromosome and comparing the impact on virulence in a mouse intraperitoneal challenge model. Mutagenesis of either the ply, lytA, or pspA gene in S. pneumoniae D39 significantly reduced virulence, r elative to that of the wild-type strain, indicating that the respective gen e products contribute to pathogenesis. On the other hand, mutations in nanA , hyl, or cbpA had no significant impact. The virulence of D39 derivatives carrying a ply deletion mutation as well as an insertion-duplication mutati on in one of the other genes was also examined. Mutagenesis of either nanA or lytA did not result in an additional attenuation of virulence in the ply deletion background. However, significant additive attenuation in virulenc e was observed for the strains with ply-hyl, ply-pspA, and ply-cbpA double mutations.