N.meningitidis Flashcards
1) classification
Family: Neisseriaceae
Genus: Neisseria
Species: meningitidis
Meningococcus
Cause life threatening sepsis
Humans are the only hosts
2) Morphology
Gram negative cocci
Usually arranged in pairs (diplococci)
Adjacent sides are flattened (kidney shaped)
Nonmotile
Non-spore forming
Most strains are capsulated
They may be intracellular (mainly) or extracellular
3) growth characteristics
Aerobic organisms Grow in atmosphere with 5% CO2 Fastidious organisms Grow only on complex media- N.gonorrhoea is more fastidious Oxidase positive Catalase positive Neisseria species are very sensitive to: - drying - chilling (temp below 37) - exposure to sunlight
4) antigenic structure
Capsular polysaccharides:
- 12 serogroups
- serogroups A, B, C, X, Y and W135 commonly cause disease
5) virulence factors
Polysaccharide capsule
Pilli
Endotoxin
IgA protease
6) diseases
Meningitis (headache and stiff neck)
Meningococcemia (septicaemia with or without meningitis):
Thrombosis of small blood vessels
Waterhouse-Friderichsen syndrome is the most severe form (high fever, shock, adrenal insufficiency, disseminated intravascular coagulation)
7) Microbiological diagnosis
DME:
- gram stained smears of CSF:
Kidney-shaped, gram-negative diplococci and PMLs
- methylene blue stain:
Kidney-shaped diplococci and PMNLs
Culture:
Chocolate agar (5% CO2): small, glisten, opaque colonies
Specific tests:
Oxidase- positive
Glucose and maltose- positive
DAD test:
Direct latex agglutination tests are useful in the immediate diagnosis of meningitis
8) treatment and prevention
Treatment
- penicillin is the drug of choice
- cefotaxime, ceftriaxone or chloramphenicol is recommended
Triple C
Prevention
- chemoprophylaxis: rifampin
- immunoprophylaxis: vaccine containing the capsular polysaccharides A, C, Y, W135 is effective in preventing epidemics of meningitis
