PYRUVATE OXIDASE, AS A DETERMINANT OF VIRULENCE IN STREPTOCOCCUS-PNEUMONIAE

Pneumococcus has been shown to bind to epithelial cells of the nasopha rynx and lung, and to endothelial cells of the peripheral vasculature. To characterize bacterial elements required for attachment to these c ell types, a library of genetically altered pneumococci with defects i n exported proteins was screened for the loss of attachment to glycoco njugates representative of the nasopharyngeal cell receptor, type II l ung cells (LC) and human endothelial cells (EC). A mutant was identifi ed which showed a greater than 70% loss in the ability to attach to al l cell types. This mutant also showed decreased adherence to the glyco conjugates containing the terminal sugar residues GalNAc beta 1-3Gal, GalNAc beta 1-4Gal and the carbohydrate GlcNAc, which are proposed com ponents of the pneumococcal receptors specific to the surfaces of LC a nd EC. Analysis of the locus altered in this mutant revealed a gene, s pxB, that encodes a member of the family of bacterial pyruvate oxidase s which decarboxylates pyruvate to acetyl phosphate plus H2O2 and CO2. This mutant produced decreased concentrations of H2O2 and failed to g row aerobically in a chemically defined medium, unless supplemented wi th acetate which presumably restores acetyl phosphate levels by the ac tion of acetate kinase, further suggesting that spxB encodes a pyruvat e oxidase. The addition of acetate to the growth medium restored the a dherence properties of the mutant indicating a link between the enzyme and the expression of bacterial adhesins. A defect in spxB correspond ed to impaired virulence of the mutant in vivo. Compared to the parent strain, an spxB mutant showed reduced virulence in animal models for nasopharyngeal colonization, pneumonia, and sepsis. We propose that a mutation in spxB leads to down-regulation of the multiple adhesive pro perties of pneumococcus which, in turn, may correlate to diminished vi rulence in vivo.