A gerbil model for rhombencephalitis due to Listeria monocytogenes

Rhombencephalitis due to Listeria monocytogenes is a frequent complication of human listeriosis, inducing a high mortality and severe neurological sequelae despite antibiotic therapy. However, there is no animal model which consistently reproduces clinical rhombencephalitis. Here, we present a model of Listeria rhombencephalitis in gerbils. Animals were inoculated in the middle ears with a low infective dose of L. monocytogenes, thus creating prolonged otitis media with persistent bacteremia. Gerbils developed a severe rhombencephalitis with circling syndrome, paresia, ataxia, rolling movements. The invasion of the central nervous system was visualized on living animals by resonance magnetic imaging and characterized by bacterial growth in the brain, reaching about 10(7) bacteria in the rhombencephalum by day 12 of infection. The histological lesions were mainly located in the brainstem, and consisted in coalescent, necrotic abscesses with perivascular sheaths, mimicking those observed in human rhombencephalitis. Bacteria were detected by electronmicroscopy inside infectious foci, either free in necrotic material or inside inflammatory cells, mainly polymorphonuclear cells. This gerbil model of Listeria rhombencephalitis will be useful to study the molecular mechanisms allowing bacteria to cross the blood-brain barrier, and to evaluate the intracerebral efficacy of antibiotics.