1. CORYNEBACTERIUM DEFINITION: @ Gram pos. rods, not branching
Non - motile, non - sporing
Not acid fast, aerobic
Facultatively anaerobic,
Catalase pos. oxidase neg.
Ferments sugars

2. SPECIES:
@ C.diphtheriae,
pathogenic.
@ Diphtheroids,
opportunistic.

3. HABITAT: @ Lives on : skin & nasopharynx @ Man is the only infected
animal.
@ Diphtheroids live in soil,
milk, plants, and skin.

4. PATHOGENSIS: @ Secretes a polypeptide, heat-labile exotoxin.
@ Pathogenesis is made by :
1- Direct invasiveness to
establish itself in throat.
2- Exotoxin inhibits protein
synthesis in host cells.

5. Exotoxin has two domains:
@ To mediate binding of toxin
to cell membrane receptors
of host cell.
@ To inhibit protein synthesis.

6. Host response :
@ Local inflammation in throat
@ Production of exudates &
pseudomembranes .
@ Production of antibody that
neutralizes the exotoxin.

7. CLINICAL FININGS:
Cutanious Diphtheria: Presents with ulcers on skin without systemic infection.
2. Systemic Infection : Presents with gray pseudomembranes on throat + fever, sore throat, and cervical adenopathy.
Complications of diphtheria are:
1- Airway obstruction.
2- Myocarditis, arrythmias, & collapse of blood circulation.
3- Recurrent laryngeal nerve palsy.

8. EPIDEMIOLOGY: @ Transmition by airborne droplets.
@ Skin is common among people
with poor skin hygiene.

9. Sources of infection :
1- Healthy throat carriers .
2- Healthy nasal carriers (more
dangerous than throat carriers)
3- Frank clinical & subclinical cases.
4- Children with diseased tonsils and
discharging ears.
5- Cow’s milk.

10. @ Traced by phage & serological typing.
Susceptible age groups :
@ 3 – 6 months infants.
@ School children.
@ Teenagers and young adults.
Sources of Infection :
@ Traced by phage & serological typing.

11. (beaded, red granules against a blue background)
LABORATORY DIAGNOSIS:
1- Specimen : Throat swabs.
2- Microscopy:
a) Gram stain: Gram positive.
b) M.B. stain for volutin, metachromatic,
polyphosphate granules
(beaded, red granules against a blue background)
c) C.diphtheriae is club shape
(wider at one end)
d) Cells are arranged in: V or L shapes,or
in a palisade (fence) shape.

12. 3- Culture:
@ Media: Loeffler medium, blood agar,
tellurite blood agar .
@ C.diphtheriae is divided into 3 types:
*Gravis: Colony flat, radially striated,
has a gray center
(Daisy flower).
*Mitis: Colony black, raised center
(fried egg).
*Intermedius: Colony smaller, has a
dark centre, light margins
(frog egg).

13. (except interrmedius type)
4- Biochemical Reactions:
Hiss serum sugars: Glu. pos, malt. pos., lactose neg. , sucrose neg.
b) Gravis ferments starch only
c) Haemolysis on blood agar
(except interrmedius type)
d) Catalase pos. , oxidase neg.

14. 5- Toxigenicity Tests:
a) Guinea pig inoculation.
b) Eleck plate: a gel diffusion
precipitation test giving
lines when organism toxin
comes in contact with
antitoxin added to plate.

15. PREVENTION:
1-Active Immunization :
@ Triple (DPT) vaccine, I.M. 3 doses .
@ Booster dose: at one year & 6 years -
repeated every 10 years.
2-Control of outbreaks :
a) Contacts throat swabs are cultured
& organism is typed by phage or
serological typing to trace source of
infection.
b) Diagnose cases clinical & bacteriological
c) Treat cases by erythromycin,& antitoxin

16. Contacts immunization history check
(i) If full vaccination & booster dose were
given within last 2 years, no further
immunization is given.
(ii) If full vaccination was given for more
than 2 years & booster dose still not
given, give the booster dose .
(iii) Close contacts not vaccinated: give both
active and passive immunization.
(iv) Screen adults by the intradermally
Shick test to detect immunity: test neg.,
give passive & active immunization.