what causes bacterial meningitis

Bacterial meningitis is caused by a bacterial infection of the meninges, the membranes surrounding the brain and spinal cord. The bacteria can reach the meninges through the bloodstream (bacteremia) or direct extension from nearby infections (such as ear or sinus infections), or through head injuries, skull fractures, or neurosurgical procedures. Common bacteria causing meningitis vary by age but include Neisseria meningitidis, Streptococcus pneumoniae, Haemophilus influenzae, Listeria monocytogenes, and group B streptococci. These bacteria invade the meninges leading to inflammation, increased intracranial pressure, and the symptoms of meningitis.