Contribution of different pneumococcal virulence factors to experimental meningitis in mice.
BACKGROUND
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.


METHODS
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.


RESULTS
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.


CONCLUSIONS
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.
Department of Medical Biotechnologies, Laboratory of Molecular Microbiology and Biotechnology (LA,M,M,B,), University of Siena and Siena University Hospital, Siena 53100, Italy. susanna.ricci@unisi.it.
Susanna
S
Ricci
Alice
A
Gerlini
Andrea
A
Pammolli
Damiana
D
Chiavolini
Velia
V
Braione
Sergio Antonio
SA
Tripodi
Bruna
B
Colombari
Elisabetta
E
Blasi
Marco Rinaldo
MR
Oggioni
Samuele
S
Peppoloni
Gianni
G
Pozzi
D000818:Animals; D016667:Bacterial Capsules / Q000235:genetics / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D004195:Disease Models, Animal; D005260:Female; D006801:Humans; D008586:Meningitis, Pneumococcal / Q000382:microbiology* / Q000401:mortality; D051379:Mice; D013296:Streptococcus pneumoniae / Q000235:genetics / Q000378:metabolism* / Q000472:pathogenicity; D037521:Virulence Factors / Q000235:genetics / Q000378:metabolism*
D001426:Bacterial Proteins; C110344:SpsA protein, Streptococcus pneumoniae; D037521:Virulence Factors; C051592:pneumococcal surface protein A