1. Corynebacterium spp Anaerobic Gram positive bacilli,
(Chinese letters appearance)
 Non motile
Non spore forming
Non capsulated
Facultative anaerobic
Catalase positive
Oxidase negative

2. Laboratory diagnosis of case
Corynebacterium diphtheriae
- Diphtheria is a childhood disease affecting the upper
respiratory tract
Laboratory diagnosis of case
1- Cultural characteristics : On BTA
2- Gram Stain
3-Catalase (+)
4- Elek’s Test

3. Laboratory diagnosis Specimen: throat swab Cultural characteristics :
On Blood Tellurite Agar BTA
–It is selective medium for isolation of C. diphtheriae (containing potassium tellurite ) which inhibiting most other pathogenic
The colonies of C. diphtheriae are small, granular, grey, and creamy with irregular edges

4. C. diphtheriae on BTA

5. Stain: gram stain:
Gram +ve, nonspore forming - bacilli
(Chinese letters appearance)

7. Elek’s Test Principle: –It is toxin/antitoxin reaction Procedure:
A strip of filter paper saturated with diphtheria antitoxin is placed on the surface of serum agar
The organism is streaked at right angels to the filter paper
Incubate the plate at 37C for 24 hrs

8. Result:
After 48 hrs incubation, the antitoxin diffusing from filter paper strip and the toxigenic strains produce exotoxin, which diffuses and resulted in lines four precipitation lines radiating from intersection of the strip and the growth of organism
Lines of precipitations
Filter paper saturated
with diphtheria antitoxin
Inoculated M.O.