Microorganisms can infiltrate the nervous system despite the brain's defenses, such as the blood-brain barrier (BBB) and blood cerebrospinal fluid barrier (BCSFB). Pathogens like bacteria, viruses, and fungi can reach the central nervous system (CNS) through various routes, leading to severe infections like meningitis. Bacterial pathogens often employ mechanisms such as antiphagocytic capsules and resistance to immune responses to survive within the CNS.