Characterization of a Listeria monocytogenes meningitis mouse model

Background: Listeria monocytogenes is a common cause of bacterial meningitis. We developed an animal model of listerial meningitis. Methods: In survival studies, C57BL/6 mice received intracisternal injections with different L. monocytogenes sequence type 1 (ST1) colony forming units per milliliter (CFU; n = 48, 10(5), 10(6), 10(7), 10(8), and 10(9) CFU/ml). Second, mice were inoculated with 10(8) CFU/ml ST1 and sacrificed at 6 h and 24 h (n = 12/group). Outcome parameters were clinical score, CFUs, cyto-and chemokine levels, and brain histopathology. Third, 84 mice were inoculated (10(9) CFU/ml ST1) to determine optimal antibiotic treatment with different doses of amoxicillin and gentamicin. Fourth, mice were inoculated with 10(9) CFU/ml ST1, treated with amoxicillin, and sacrificed at 16 h and 24 h (n = 12/group) for outcome assessment. Finally, time point experiments were repeated with ST6 (n = 24/group). Results: Median survival time for inoculation with 10(8) and 10(9) CFU/ml ST1 was 46 h and 40 h; lower doses of bacteria led to minimal clinical signs of disease. Brain levels of IL-6, IL-17A, and IFN-gamma were elevated at 24 h, and IL-1 beta, IL-6, IL-10, IFN-gamma, and TNF-alpha were elevated in blood at 6 h and 24 h. Histopathology showed increased meningeal infiltration, vascular inflammation of meningeal vessels, hemorrhages, and ventriculitis. In the treatment model, brain levels of IL-6 and IL-17A and blood levels of IL-6 and IFN-gamma were elevated. Compared to ST6, infection with ST1 led initially to higher levels of IL-1 beta and TNF-alpha in blood and more profound neuropathological damage. At 16 h post inoculation, IL-1 beta, IL-10, and TNF-alpha in blood and IL-6, IL17A, TNF-alpha, and IFN-gamma levels in brain were higher in ST1 compared to ST6 without differences in CFUs between STs. At 24 h, neuropathology score was higher in ST1 compared to ST6 (p = 0.002) infected mice. Conclusions: We developed and validated a murine model of listerial meningitis. ST1-infected mice had a more severe inflammatory response and brain damage as compared to ST6-infected mice.