The three extra-cellular zinc metalloproteinases of Streptococcus pneumoniae have a different impact on virulence in mice

Background: Streptococcus pneumoniae possesses large zinc metalloproteinases on its surface. To analyse the importance in virulence of three of these metalloproteinases, intranasal challenge of MF1 outbred mice was carried out using a range of infecting doses of wild type and knock-out pneumococcal mutant strains, in order to compare mice survival. Results: Observation of survival percentages over time and detection of LD₅₀s of knock out)mutants in the proteinase genes in comparison to the type 4 TIGR4 wild type strain revealed two major aspects: i) Iga and ZmpB, present in all strains of S. pneumoniae, strongly contribute to virulence in mice; (ii) ZmpC, only present in about 25% of pneumococcal strains, has a lower influence on virulence in mice. Conclusions: These data suggest Iga, ZmpB and ZmpC as candidate surface proteins responsible for pneumococcal infection and potentially involved in distinct stages of pneumococcal disease.