MICROBIOLOGY PPT LECTURE NOTES | Karya Tulis Ilmiah

Corynebacterium diphtheriae

Biological
Features
 Aerobic,

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

Chinese-letter morphology in Gram stain

Transmission and Risk fact
 solely

ors

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 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

 Thick

grey
‘pseudomembrane’
composed of fibrin,
epithelial cells,

bacteria and
polymorph
neutrophils
 Pseudomembrane
may cause blockage,
suffocation

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

Epidemiology
 Largely controlled
 However,

now by vaccination

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

world

Immunity
 Immunization

of animals with altered toxin, pr
oducing antitoxin, was first done in 1890, 1st
used in humans in 1891
 Toxin-antitoxin introduced by Theobald Smit
h in 1909, used little
 Toxoid introduced in 1923, now widely used

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.

DIAGNOSIS
 Clinical:

Muscle weakness, edema and a pseu
domembranous material in the upper respirator
y tract characterizes diphtheria.
 Laboratory: Tellurite media is the agar of cho
ice for isolation of Corynebacteria, which prod
uce jet black colonies

Control
 Sanitary: Reduce carrier rate by use of vac

cine.

 Immunological: A vaccine (DPT) prepare

d from an alkaline formaldehyde inactivated t
oxin (i.e. toxoid) is required. Passive immuni

zation with antitoxin can be used for patients.
 Chemotherapeutic: Penicillin, erythromy
cin or gentamicin are drugs of choice.

Prospect
For therapy of tumors !

!
tumor
Ab

DT