Essential role of choline for pneumococcal virulence in an experimental model of meningitis

Objectives: The goal of the present study was to elucidate the contribution of the newly recognized virulence factor choline to the pathogenesis of Streptococcus pneumoniae in an animal model of meningitis. Results: The choline containing strain D39Cho^– and its isogenic choline‐free derivative D39Cho^–licA64 –each expressing the capsule polysaccharide 2 – were introduced intracisternally at an inoculum size of 10³ CFU into 11 days old Wistar rats. During the first 8 h post infection both strains multiplied and stimulated a similar immune response that involved expression of high levels of proinflammatory cytokines, the matrix metalloproteinase 9 (MMP‐9), IL‐10, and the influx of white blood cells into the CSF. Virtually identical immune response was also elicited by intracisternal inoculation of 10⁷ CFU equivalents of either choline‐containing or choline‐free cell walls. At sampling times past 8 h strain D39Cho^– continued to replicate accompanied by an intense inflammatory response and strong granulocytic pleiocytosis. Animals infected with D39Cho^– died within 20 h and histopathology revealed brain damage in the cerebral cortex and hippocampus. In contrast, the initial immune response generated by the choline‐free strain D39Cho^–licA64 began to decline after the first 8 h accompanied by elimination of the bacteria from the CSF in parallel with a strong WBC response peaking at 8 h after infection. All animals survived and there was no evidence for brain damage. Conclusion: Choline in the cell wall is essential for pneumococci to remain highly virulent and survive within the host and establish pneumococcal meningitis.