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

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

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

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.

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

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

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.

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

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.

@ 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.

(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.

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).

(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.

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.

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

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.