113lecture3006

113lecture3006 - BIOLOGY 113 - MICROBIOLOGY Lecture 30:...

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BIOLOGY 113 - MICROBIOLOGY Lecture 30: Microbial Diseases of the Nervous System Unlike the skin, the central nervous system and peripheral nervous system have no native flora - Surrounding the brain and spinal cord are a set of continuous membranes, the meninges ; cerebrospinal fluid circulates between the two innermost meninges (Tortora et al., Figure 22.2) - An interesting feature of the central nervous system, with revelance to infection, is the blood- brain barrier = Tissues of the central nervous system are served by specialized capillaries that are more selective than most capillaries in allowing passage of molecules = As a result, many antimicrobial drugs are unable to reach the tissues of the central nervous system, complicating treatment = On the other hand, the blood-brain barrier may serve as a nonspecific defense against infection - Microorganisms may infect the central nervous system = Trauma can interrupt the normal barriers, and some microorganisms move along peripheral nerves = The most common route for infection of the central nervous system is probably through lymphatic vessels - Infection of the meninges is called meningitis , while infection of the brain itself is called encephalitis Bacterial meningitis can be caused by a variety of bacteria, especially is trauma allows introduction of normal flora or environmental material to the central nervous system; however, greater than 80% of cases are caused by three species (Tortora et al. Table 22.1): - Nesseria meningitidis , the agent of meningococcal meningitis , is found as part of the respiratory tract flora of some persons = Throat infection of a susceptible host can lead to bacteremia, then to invasion of the cerebrospinal fluid = N . meningitidis resists killing by phagocytes, which may aid its invasion of the central nervous system = Pathogenesis of meningococcal meningitis is related to the effects of N . meningitidis endotoxin = In the past, outbreaks of meningococcal meningitis were common in military training facilities = Concern with outbreaks at colleges has led to more widespread use of a vaccine for meningococcal meningitis - Haemophilus influenzae was once an important agent of bacterial meningitis in young children
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113lecture3006 - BIOLOGY 113 - MICROBIOLOGY Lecture 30:...

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