Pathology Spotlight: Brain attack – Bacterial meningitis

Continuing our blog series of posts entitled “Pathology Spotlight”,  a new regular feature where we will be sharing content describing interesting specimens from our collection with an emphasis on the patho-physiological process.

The brain is covered with three layers of protective membranes known collectively as the meninges. These membranes can become infected causing meningitis, a life-threatening condition affecting 3,200 people in Britain every year. There is no single cause; meningitis can arise from a bacterial infection such as Neisseria meningitidis (also called Meningococcus), E.coli or Streptococcus moving from the nose or throat to the brain, or from a virus like herpes, chicken pox, measles or mumps. However the single most common cause of bacterial meningitis is the Meningococcus.  Many microbes can reach the blood but few can gain access from there to the brain. Meningococci achieve this through hair-like structures on their surface called pili, which act like tiny hooks enabling them to stick specifically to the cells that line the blood vessels of the brain. While microorganisms in the blood that don’t possess such pili pass straight through the brain blood vessels in the blood-flow, the meningococci use their pili to adhere to the lining cells. This adherence also produces minute gaps between the lining cells, which the meningococci then squeeze through gaining access to the meninges. There these bacteria proliferate, causing meningitis. The most harmful Meningococci are also surrounded by a thick sugary capsule which protects these bacteria from being killed by the cells of the immune system which attack them.

Neisseria_meningitidis
The white blobs across the top left of the plate are colonies of Meningococci growing in culture

 

Bacterial meningitis is usually more serious than viral meningitis, and can lead rapidly to septicaemia and death. The specimen shown here displays meningococcal meningitis. The folds of the brain surface are almost completely obscured by a thick, white layer of pus caused by the infection in the membranes overlying them. Only a few small areas of pink, normal brain can be seen. While meningitis can affect all age groups, infants and children are most at risk. Early medical attention greatly improves the chance of successful treatment, so awareness of symptoms is very important. These include headaches, fever, and a rash which doesn’t fade when a glass is rolled over it, along with photo-phobia and convulsions.

gc 8535
A brain with Meningococcal meningitis

 

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