The normal biota of the central nervous system includes
Neisseria meningitidis
Herpes simplex I
Herpes simplex II
Streptococcus agalactiae
The CNS has no normal biota.
The correct answer and explanation is :
The correct answer is:
The CNS has no normal biota.
Explanation:
The central nervous system (CNS), which includes the brain and spinal cord, is typically considered to be a sterile environment. Under normal conditions, the CNS does not harbor any microbiota (microorganisms such as bacteria, viruses, or fungi) that can be classified as “normal.” This is due to the presence of several protective barriers, such as the blood-brain barrier and the cerebrospinal fluid (CSF), which help prevent microorganisms from entering the CNS.
Microorganisms listed in the options, such as Neisseria meningitidis, Herpes simplex I, Herpes simplex II, and Streptococcus agalactiae, can cause infections in the CNS, but they are not part of the normal microbiota of the CNS. When these pathogens enter the CNS, they can lead to serious conditions such as meningitis, encephalitis, and other neurological disorders.
- Neisseria meningitidis is a bacterium that can cause meningococcal meningitis, a life-threatening infection of the meninges (the protective membranes covering the brain and spinal cord).
- Herpes simplex virus type I (HSV-1) is associated with oral herpes but can also cause viral encephalitis, particularly in immunocompromised individuals.
- Herpes simplex virus type II (HSV-2) is typically associated with genital infections but can also cause CNS infections, including neonatal herpes with encephalitis.
- Streptococcus agalactiae, also known as Group B Streptococcus, is a common cause of meningitis in neonates.
While these organisms may occasionally be present in other parts of the body (such as the respiratory or genital tract), they are not part of the normal biota of the CNS. The concept of “normal biota” refers to the microbes that live in symbiosis with the host without causing disease, and this does not extend to the CNS under healthy, non-infected conditions. Therefore, under normal circumstances, the CNS is free from microorganisms, and the presence of any pathogen is considered abnormal and can lead to infections.