Final answer:
Endothelial cells of the blood-brain barrier (BBB) are most responsible for preventing bacteria from entering the brain fluids. During meningitis, it is these cells that are initially disrupted. Glial cells, like ependymal cells, contribute to CNS health by producing CSF but are not primarily responsible for maintaining the barrier's integrity.
Step-by-step explanation:
The cells most responsible for preventing bacteria from entering the fluids of the brain are the endothelial cells of the blood-brain barrier (BBB). The BBB is a selective membrane that filters what enters the central nervous system (CNS). Its primary role is to allow necessary substances such as water, gases, glucose, and amino acids to pass while keeping out potentially harmful substances such as microbes and toxins. The endothelial cells form tight junctions that control the passage of components from the blood into the brain. When infection such as meningitis occurs, it is primarily these cells whose function is disrupted, allowing pathogens to infiltrate the CNS and cause inflammation.
Glial cells, specifically the ependymal cells, are also pivotal in CNS protection. They filter blood to create cerebrospinal fluid (CSF), which then circulates throughout the CNS, but are not directly responsible for the integrity of the BBB.
Meningitis and the Blood-Brain Barrier
In cases of meningitis, a viral or bacterial infection of the brain, it is generally the endothelial cells' function that is first compromised. Some pathogens have unique virulence factors that enable them to breach the BBB. Once the BBB is compromised, pathogens spread to the meninges and CNS tissue, leading to serious conditions such as encephalitis or meningitis.