Brain Infection by Group B Streptococcus Induces Inflammation and Affects Neurogenesis in the Adult Mouse Hippocampus

Central nervous system infections caused by pathogens crossing the blood-brain barrier are extremely damaging and trigger cellular alterations and neuroinflammation. Bacterial brain infection, in particular, is a major cause of hippocampal neuronal degeneration. Hippocampal neurogenesis, a continuous multistep process occurring throughout life in the adult brain, could compensate for such neuronal loss. However, the high rates of cognitive and other sequelae from bacterial meningitis/encephalitis suggest that endogenous repair mechanisms might be severely affected. In the current study, we used Group B Streptococcus (GBS) strain NEM316, to establish an adult mouse model of brain infection and determine its impact on adult neurogenesis. Experimental encephalitis elicited neurological deficits and death, induced inflammation, and affected neurogenesis in the dentate gyrus of the adult hippocampus by suppressing the proliferation of progenitor cells and the generation of newborn neurons. These effects were specifically associated with hippocampal neurogenesis while subventricular zone neurogenesis was not affected. Overall, our data provide new insights regarding the effect of GBS infection on adult brain neurogenesis.