Corynebacteria

Question 1

Pathogenic species (3)

Answer 1

1- Corynebacterium diphtheriae —> Causes diphtheria

2- Corynebacterium ulcerans —> Zoonotic

3- Corynebacterium psuedotuberculosis —> Lymphadenitis in sheep and goat

Question 2

Non-pathogenic species (1)

Answer 2

Diphtheroid (common specimen contaminant)

Question 3

C.diphtherae Common Characteristics (3)

Answer 3

1- Gram-positive (stain unevenly)

2- Pleomorphic bacilli that form characteristic clumps (look like Chinese characters or Picket fence)

3- Facultative anaerobes

(Nom-motile, Non-capsulated)

Question 4

C.diphtherae Cultivation

Answer 4

Culture aerobically on selective medium e.g. Tinsdale agar (contains Potassium tellurite)

Question 5

Transmission

Answer 5

Respiratory droplets

Question 6

Diphtheria Toxin (3)

Answer 6

EXOTOXIN inhibits eukaryotic PROTEIN SYNTHESIS

(Inactivates Eukaryotic polypeptide chain ELONGATION FACTOR EF-2 by ADP-RIBOSYLATION resulting in termination of protein synthesis)

(Gene for toxin encoded by bacteriophage —> those with the gene are lysogenic and so virulent)

Question 7

Diphtheria Disease Characteristics (3)

Answer 7

Starts as local infection of THROAT

Produces thick, grayish, adherent exudate (PSEUDOMEMBRANE) that coats throat and may extend to nasal passages. Sometimes obstructs airway —> SUFFOCATION

Major clinical effects involve HEART damage, and PERIPHERAL NERVES (neuritis of cranial nerves and paralysis of muscle groups that control movement of palate and eye)

Question 8

Diphtheria Treatment (3)

Answer 8

1- Horse serum Antitoxin (side effect - serum sickness)

2- Erythromycin or Penicillin

3- DPT vaccine (booster = 10 years)

Question 9

Diphtheria Laboratory Diagnosis

Answer 9

Initial diagnosis by CLINICAL OBSERVATION as no reliable rapid laboratory test available

Isolate tested for TOXIN production using Immunologic Perciptin Reaction (Elek Test)

Question 10

Diphtheroid (2)

Answer 10

Morphologically resemble C.diphtheriae

Only disease in Immunocompromised:
1- Infective endocarditis of prosthetic valves, lung abscess, UTI

2- Multiple drug resistant

Question 11

Molecular Typing C.diphtheriae (5)

Answer 11

Ribotyping 
Pulse-field Gel Electrophoresis
DNA Sequencing 
Random Amplified Polymorphism of DNA
Multi-locus Enzyme Electrophoresis