Properties

Pathogenesis

Clinical findings

Laboratory diagnosis

Treatment & Prevention

Gram negative cocci.

Seen in pairs (diplococci)

Contain endotoxin in outer membrane.

Growth is inhibited by toxic trace metals & fatty acids.

Oxidase-positive.

Carried in the nasopharynx of man.

Spread mainly by respiratory droplets or close contact.

Common cause of bacterial meningitis together with H.influenzae & Streptococcus pneumoniae; most likely to cause epidemics of meningitis.

Virulence factors:

- polysaccharide capsule (common types A, B & C): resistance to phagocytosis by PMNs.

- endotoxin causes fever, shock.

- IgA protease helps bacteria to attach to membranes of upper respiratory tract.

Properties of polysaccharide capsule:

- enhances virulence by its antiphagocytic action.

- defines serologic groups.

- detected in spinal fluid of patients with meningitis.

- antigen in the vaccine.

Meningococcal septicaemia:

- invasion of bloodstream by bacteria.

- patient develops fever, shock & usually a skin rash.

- patient is unwell & depression of cerebral function becomes evident: from drowsiness to coma.

- characteristic rash: petechial developing into purpura.

Waterhouse-Friderichsen syndrome:

- high fever

- shock

- widespread purpura

- disseminated intravascular coagulation.

- adrenal insufficiency

- bacteremia results in seeding of many organs.

Meningcoccal meningitis:

- fever

- headache

- stiff neck

- increased level of PMNs in spinal fluild.

Smear, culture of blood & spinal fluid samples.

CSF show presence of Gram negative diplococci mostly inside PMNs.

Latex agglutination test detects capsular polysaccharide in spinal fluid.

Differentiating N.meningitis from N.gonorrhoeae:

- basis of sugar fermentation test.

- meningococci ferments maltose while gonococci do not.

Benzylpenicillin, but does not clear throat carriage.

Prophylaxis: rifampicin & ciprofloxacin.

Vaccination:

- covers groups A & C.

- made from purified capsular polysaccharide

Indications for use:

- splenectomy

- travel to areas where infection is common, includes Haj pilgrims.

- local outbreaks of infection.