Acute bacterial meningitis

Question 1

Background

Answer 1

The CNS is protected both by a three membrane barrier called the meninges and by immune cells within those membranes
-the CNS is also walled off from the rest of the body by specialised blood vessels that are tightly sealed by the blood brain barrier

Question 2

Spread

Answer 2

• sneezing
• coughing
• kissing

meningitis is usually caught from people who carry their viruses or bacteria in their nose or throat but are not ill themselves

infection spreads from mucosal surfaces via the bloodstream and causes infection in the meninges

Question 3

How organisms can reach the brain

Answer 3

• head trauma / surgery
• sinuses / ear infections
• RTI
• infective endocarditis

Question 4

Three classical bacterial causes of bacterial meningitis

Answer 4

• Neisseria meningitidis
• Streptococcus pneumoniae
• Hemophilus influenzae type B

Question 5

What happens in infective meningitis

Answer 5

Albumin enters the CNF - toxins from bacteria and neutrophils together with reduced O2 and nutrients enters the brain cells - oedema and brain swelling - stops CSF entering the brain

• circulatory failure
• bacterial toxins can damage blood vessels and organs
• blood leaks in tissues often causing a skin rash
• tissue starved of oxygen

Question 6

Clinical manifestations

Answer 6

Non Specific = high fever, vomiting, lethargy, refusing food and drink, severe muscle pain, severe headache

More specific = stiff neck/back, photophobia, seizures, cold hands and feet

Question 7

Ability to penetrate CSF/meninges

Answer 7

• penetrate even when meninges are not inflamed = chloramphenicol, metronidazole, isoniazid, pyrazinamide
• penetrate inflamed meninges and used in high doses= most beta lactams, quinolones, rifampicin

Penetrate poorly but better when inflamed = vancomycin

Penetrate poorly = gentamicin

Question 8

Prevention

Answer 8

• pool of healthy carriers
• vaccination
• prophylaxis on significant exposure

Question 9

Neisseria meningitidis

Answer 9

• gram negative diplococcus
  -aerobic
• oxidase positive
• can be encapsulated or nonencapsulated
• transmission through droplets

N. Meningiditis resides on the upper respiratory mucosa. The first stage of infection involves bacteria passing through to the bloodstream through endocytosis and them migrating to the blood brain barrier. It then passes through the blood brain barrier to cause meningitis

• N.meningitidis survives in the bloodstream using its capsule
• N.meningitidis attaches to brain endothelial cells using type IV pili, allowing microcolony formation
• the lipooligosaccharide binds to monocytes and dendritic immune cells to trigger release of cytokines resulting in endothelial damage and capillary leakage
• activates host signalling pathways resulting in the opening of intracellular junctions
• meningococcus passes through and proliferates to cause infection

Question 10

Listeria monocytogenes

Answer 10

• gram positive rod which is highly flagilated
• catalase positive
• Beta haemolytic
• it is found in soil, water and animal faeces
• commonly acquired from contaminated food
• currently no vaccines available

-expresses surface proteins that allow it to gain entry into epithelial and immune cells through endocytosis/phagocytosis
- when enclosed, the low pH activates the exotoxin listeriolysin O causing the release of the bacteria
- the bacteria associate with the host actin and move towards the cell membrane where they can be taken up by the neighbouring cell
- the bacteria are never exposed to the outside of the cells avoiding immune responses
-they can use this mechanism to pass through the meninges and blood brain barrier to cause meningitis