Corynebacterium diphtheriae

Corynebacterium diphtheriae

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Chapter NO # 07
Corynebacterium Diphtheriae
Biological Features
 Aerobic, Gram
+
, Noncapsulated, rods
 Gray-black colonies on tellurite medium
 Metachromatic granules



Transmission and Risk factors
 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

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Chapter NO # 07



Pathogenesis of diphtheria



 Early stages: Sore throat. Low fever. Swollen neck glands.
 Late stages: Airway obstruction and breathing difficulty. Shock
Diphtheria Toxin (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

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Chapter NO # 07

Immunity
 Immunization of animals with altered toxin, producing 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
DIAGNOSIS
Clinical: Muscle weakness, edema and a pseudomembranous 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.

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Chapter NO # 07


Tellurite Blood Agar
 Tellurite Blood Agar is a selective medium used for isolation and cultivation of Corynebacterium
species.
 Potassium tellurite acts as a selective agent and has inhibitory activity against most gram-positive
and gram-negative bacteria except Corynebacterium species.
 C.diphtheriae reduces potassium tellurite to tellurium and thereby produce gray-black coloured
colonies.
Control
 Sanitary: Reduce carrier rate by use of vaccine.
 Immunological: A vaccine (DPT) prepared 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.


Prepared By
Amjad Khan Afridi
Date: 18
th
March, 2017