Neisseria Meningitidis

CLASSIFICATION:

• Family: Neisseriaceae
• Genus: Neisseria
• Species: Neisseria Meningitidis

MORPHOLOGY:

• Gram negative diplococcus (paired)
• Size: 0.6-0.8 ?m
• Bean shaped
• Non-motile
• Aerobe
• Encapsulated

BIOCHEMICAL PROPERTIES:

• Oxidase positive
• Catalase positive
• Ferments glucose and maltose with acid production
  • Differentiating feature of Neisseria gonococcus from Neisseria meningitides
• Gamma-glutamyl aminopeptidase positive
• Production of Deoxyribonuclease (DNAse)
• Nitrate negative
• Doesn’t ferment lactose, sucrose and fructose
• Colistin resistant

SEROGROUPS:

• N. Meningitidis has been divided into atleast 13 serogroups on the basis of specificity of capsular polysaccharide antigens.
• These are A,B,C,D,X,Y,Z,W 135,29E,H,I,K and L. 
• Serogroups A,B,C,X,Y,W 135 are most commonly associated with meningococcal disease.

VIRULENCE  FACTORS:

Adhesion factors :

•  Pili for adhesion to mucosa of oropharynx and meningeal tissue

Capsule : 

• Antiphagocytic

Lipopolysaccharide : 

• Endotoxin
• Responsible for the production of overwhelming septicemic shock complicating bacteremia

IgA proteases :

•  cleaves IgA protecting organism from effects of secretory IgA

EPIDEMIOLOGY:

Natural habitat and reservoir : 

• Mucosal surfaces of the human nasopharynx, urogenital tract and anal canal

Nasopharyngeal carriers : 

• Approximately 5-10% adults are asymptomatic carriers (may reach 90% in close communities)

Modes of infection:

• Direct contact or respiratory droplets from the nose and throat of infected people
• Most common organism which can contaminates crowded army camps

PATHOGENESIS:

1. Inhalation of contaminated droplets
2. Adherence of organism to nasopharyngeal mucosa
3. Local invasion and spread from nasopharynx to meninges through blood stream
4. In meninges, organsims are internalised into phagocytic cells
5. They replicate and migrate to subepithelial spaces
6. Incubation period : 3-4 days

CLINICAL FEATURES:

Febrile illness :

• Mild and self limiting

Pyogenic meningitis : 

• Most common cause of meningitis in children
• High fever, stiff neck, Kernig’s sign, severe headache, vomiting, photophobia, chills

Meningiococcal septicemia :

• Acute fever with chills, malaise, prostration, Waterhouse-frederichsen syndrome, DIC

Other Syndrome :

•  Pneumonia, arthritis, urethritis, respiratory tract infection

PROPHYLAXIS:

Chemoprophylaxis :

• Rifampicin
• Minocycline
• Ciprofloxacin

Vaccination:

• A vaccine containing capsular polysaccharide of serotypes A and C : for infants below 2 years
• A quadrivalent vaccine constituted by polysaccharides of serotypes A,C,Y and W-135 : for children and adults

Specimen:

• CSF
• Blood

 Examination of CSF:

• Increased Pressure
• Turbid
• The collected CSF is divided into 3 portions (for microscopy, for biochemical tests and for culture)

Microscopy:

• Gram stained smear of CSF deposit commonly shows Gram negative intracellular diplococci.
• White cell count increases to several thousand per cubic mm with 90-99% PMNs.

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