corynebacterium dephtheriae جيد
DESCRIPTION
ÂTRANSCRIPT
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 !!