Contribution of different pneumococcal virulence factors to experimental meningitis in mice
1 Department of Medical Biotechnologies, Laboratory of Molecular Microbiology and Biotechnology (LA.M.M.B.), University of Siena and Siena University Hospital, Siena 53100, Italy
2 Department of Physiopathology, Experimental Medicine and Public Health, University of Siena, Siena, Italy
3 Department of Pathology, Siena University Hospital, Siena, Italy
4 Department of Diagnostics, Clinical and Public Health Medicine, University of Modena and Reggio Emilia (Unimore), Emilia-Romagna, Italy
5 Present address: Evans Medical Research Center, Boston University School of Medicine, 650 Albany Street, Boston, MA 02118, USA
6 Present address: Sanofi-Aventis S.p.a., Brindisi 72100, Italy
BMC Infectious Diseases 2013, 13:444 doi:10.1186/1471-2334-13-444Published: 24 September 2013
Pneumococcal meningitis (PM) is a life-threatening disease with a high case-fatality rate and elevated risk for serious neurological sequelae. In this study, we investigated the contribution of three major virulence factors of Streptococcus pneumoniae, the capsule, pneumococcal surface protein A (PspA) and C (PspC), to the pathogenesis of experimental PM.
Mice were challenged by the intracranial route with the serotype 4 TIGR4 strain (wt) and three isogenic mutants devoid of PspA, PspC, and the capsule. Survival, bacterial counts, and brain histology were carried out. To study the interaction between S. pneumoniae mutants and microglia, phagocytosis and survival experiments were performed using the BV2 mouse microglial cell line.
Virulence of the PspC mutant was comparable to that of TIGR4. In contrast, survival of animals challenged with the PspA mutant was significantly increased compared with the wt, and the mutant was also impaired at replicating in the brain and blood of infected mice. Brain histology indicated that all strains, except for the unencapsulated mutant, caused PM. Analysis of inflammation and damage in the brain of mice infected with TIGR4 or its unencapsulated mutant demonstrated that the rough strain was unable to induce inflammation and neuronal injury, even at high challenge doses. Results with BV2 cells showed no differences in phagocytic uptake between wt and mutants. In survival assays, however, the PspA mutant showed significantly reduced survival in microglia compared with the wt.
PspA contributed to PM pathogenesis possibly by interacting with microglia at early infection stages, while PspC had limited importance in the disease. The rough mutant did not cause brain inflammation, neuronal damage or mouse death, strengthening the key role of the capsule in PM.