Corynebacterium diphtheriaeCorynebacterium diphtheriae

Biological Biological FeaturesFeatures

Aerobic, Gram+, Noncapsulated, rods Gray-black colonies on tellurite亚碲酸盐 medium Metachromatic granules

Chinese-letter morphology in Gram stain

Transmission and Transmission and Risk factRisk factorsors solely among humans spread by droplets secretions direct contact

Poor nutrition Crowded or unsanitary

living conditions Low vaccine coverage

among infants and children

Immunity gaps in adults

Pathogenesis of diphtheriaPathogenesis of diphtheria

Early stages: Sore throat. Low fever. Swollen neck glands.

Late stages: Airway obstruction and breathing difficulty. Shock

Diphtheria Toxin Diphtheria Toxin (DT)(DT) Cleaved to yield A/B fragment, joined by S-S bond

- A (catalytic domain) - B (transmembrane and receptor binding domains) Receptor: heparin-binding epidermal growth factor - rich on cardiac cells and nerve cells Toxin diffuses throughout body via blood

- Cardiac, neurologic complications - Heart/respiratory damage, paralysis

Thick grey ‘pseudomembrane’composed of fibrin, epithelial cells, bacteria and polymorph neutrophils

Pseudomembranemay cause blockage, suffocation

The cervical lymph nodes enlarge causing The cervical lymph nodes enlarge causing oedemaoedemaof the neck (a classical condition of of the neck (a classical condition of ‘‘bullneckbullneck’’))

Largely controlled now by vaccination

However, factors such as poverty and other social factors have led to diphtheria being an endemic/epidemic in many regions of the world

EpidemiologyEpidemiology

ImmunityImmunityImmunization of animals with altered toxin, pr

oducing antitoxin, was first done in 1890, 1st used in humans in 1891

Toxin-antitoxin introduced by Theobald Smith in 1909, used little

Toxoid introduced in 1923, now widely used

Schick testSchick testBe used to ascertain population risk This test involves the injection of a minute amount of the diphtheria toxin under the skin. The absence of a reaction

indicates immunity.

DIAGNOSISDIAGNOSISClinical: Muscle weakness, edema and a pseu

domembranous material in the upper respiratory tract characterizes diphtheria.

Laboratory: Tellurite media is the agar of choice for isolation of Corynebacteria, which produce jet black colonies

ControlControlSanitary: Reduce carrier rate by use of vac

cine. Immunological: A vaccine (DPT) prepare

d from an alkaline formaldehyde inactivated toxin (i.e. toxoid) is required. Passive immunization with antitoxin can be used for patients.

Chemotherapeutic: Penicillin, erythromycin or gentamicin are drugs of choice.

ProspectProspect

For therapy of

AbDT

tumor

tumors !!