Molecular mechanisms of bacterial infections of the central nervous system.

Central nervous system (CNS) infections may involve the meninges, brain and/or spinal cord. The most common etiologic agents are Streptococcus pneumoniae, group B Streptococci, Neisseria meningitidis, Haemophilus influenzae, and Listeria monocytogenes. CNS is characterized by specific structure and function. Despite a unique system of brain barriers and autonomous immune system, CNS is very susceptible to microorganisms which may invade directly, via the blood, or less frequently by reverse axonal transport. The complex process of bacteria and activated polymorphonuclear leukocyte transfer to the subarachnoid space, which is devoid of natural immune defence mechanisms, initiates an inflammatory response that subsequently spreads to the brain tissue. Consequences of these changes include damage to the blood-brain barrier, development of vasogenic cerebral oedema, and intracranial pressurevolume disturbances leading to impaired CNS perfusion.