Corynebacterium diphtheriae

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Corynebacterium diphtheriae

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Biological Features

• Aerobic, Gram, Noncapsulated, rods
• Gray-black colonies on tellurite????medium
• Metachromatic granules

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Chinese-letter morphology in Gram stain
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Electron micrograph of corynebacteriophage ß,
which carries tox
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Transmission

• solely among humans
• spread by droplets
• secretions
• direct contact

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Risk factors

• Poor nutrition
• Crowded or unsanitary living conditions
• Low vaccine coverage among infants and children
• Immunity gaps in adults

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Pathogenesis of diphtheria

• Early stages Sore throat. Low fever. Swollen
  neck glands.
• Late stages Airway obstruction and breathing
  difficulty. Shock

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Diphtheria Toxin (DT)

• Cleaved to yield A/B fragment, joined by S-S
  bond- A (catalytic domain)
• - B (transmembrane and receptor binding
  domains)

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Diphtheria Toxin (DT)

• 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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Schematic diagram of the diphtherial intoxication
of a sensitive eukaryotic cell.
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• Thick grey pseudomembrane composed of fibrin,
  epithelial cells, bacteria and polymorph
  neutrophils
• Pseudomembrane may cause blockage, suffocation

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(No Transcript)
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The cervical lymph nodes enlarge causing oedema
of the neck (a classical condition of bullneck)

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Epidemiology

• 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

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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

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Schick test

• Be 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.

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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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Elek immunodiffusion test.
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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.

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Prospect
tumors !!

• For therapy of

tumor
Ab
DT