MICROBIOLOGICAL DIAGNOSIS OF CORYNEBACTERIUM DIPHTHERIA

1. CORYNEBACTERIUM
DIPHTHERIAE
FAMILY: CORYNEBACTERIACEAE

2. 
Morphology
Antigenic structure
Virulence factors
Pathogenesis
Diseases
Treatment and prevention
Microbiological examination
OUTLINE

3. 
 Non motile, non spore forming
 Not encapsulated
 Club shaped
 Aerobic, Gram (+) rod bacillus
 Metachromatic granules are distributed within the rod
to give it a beaded appearance.
MORPHOLOGY

4. 
ANTIGENIC STRUCTURE

5.  The plasma membrane of these bacteria is covered by a
peptidoglycan layer, which itself is covalently linked to
arabinogalactan, an additional heteropolysaccharide
meshwork.
 Bound to this, an outer layer of mycolic acid-
corynemycolic acid is found.
 As top layer, outer surface material composed of free
polysaccharides, glycolipids, and proteins (including S-
layer proteins, pili, and other surface proteins)

6. 
 Diphtheria toxin
 Inhibits protein synthesis
 Carries the tox gene from a beta-phage
 Dermonecrotic toxin
 Increases vascular permeability
 Hemolysin
 Cord factor- Toxic trehalose
 Corynemycolic and Corynemycolenic acid
VIRULENCE FACTORS

7. PATHOGENESIS

8. 
 Asymptomatic nasopharyngeal carriage is common
in regions where diphtheria is endemic.
 Toxigenic strains in susceptible individuals can cause
disease by multiplying and secreting diphtheria toxin
into either skin or nasopharyngeal lesions.
 The diphtheritic lesion is often covered by a
pseudomembrane composed of fibrin, bacteria, and
inflammatory cells.

9. 
DISEASES
Respiratory diphteria

10. 
Cutaneous diphtheria

11.  Diphtheria vaccine is usually combined at least with
tetanus (Td) and often with pertussis (DTP, DTaP, TdaP)
vaccines for infants during immunization.
 Obstruction in the throat may require intubation or a
tracheotomy.
 Antitoxins in addition to:
 Metronidazole
 Penicillin G
 Erythromycin can also be administered
PREVENTION AND
TREATMENT

12. MICROBIOLOGICAL
EXAMINATION
 They grow on:
 Loffler’s medium-
yellowish white colonies
 Blood agar
 Tellurite medium-
gray/black colonies

13. 
C. diphtheriae gives subspecies when grown
in Tellurite medium:
 C. gravis
 C. intermedius
 C. mitis