Corynebacterium diphtheriae

About

• Rarely seen. Check vaccination history

Characteristics

• Gram positive, club-shaped, non-motile rods growing at angles forming V,L,W shapes "Chinese letter shapes"
• Grows best with oxygen at 37 degrees
• Exotoxin only produced by those with the relevant phage
• Exotoxin has two components A and B as described below

Source

• Human reservoirs - respiratory tract

Virulence

• Those bacteria infected with the corynephage beta produces an A-B toxin
• The A component is an ADP ribosyl transferase that binds to eukaryotic elongation factor 2 blocking protein synthesis
• The B component directs the toxin to the oropharynx, heart and nerve cells

Pathogenicity

• Pharyngitis - grey dirty pseudomembrane is visibly composed of fibrin and dead cells and there is associated lymphadenopathy producing a "bull neck"
• Myocarditis and cardiac dysfunction - bradycardia, chest pain
• Laryngeal nerve palsy - hoarseness

Investigations

• Grows on Hoyle's media (Blood tellurite) producing black colonies reducing tellurite to tellurium. An alternative is the Tinsdales medium with added horse serum.
• There are 3 types - gravis (worst), intermedius, mitis (best) which suggest the severity of disease caused and can be separated by haemolysis and appearance
• Biochemical testing for catalase, urease, nitrate, pyranzinamidase, cystinase
• Test for toxin production using Elek test using antitoxin
• Serotyping and bacteriophage typing

Vaccination

• Prevention with vaccination with diphtheria toxoid

Sensitivities

• Penicillin or Erythromycin

Toxin

• Give antitoxin

Management

• Penicillin or Erythromycin
• Antitoxin
• Contacts given Erythromycin as prophylaxis
• Diphtheria immunisation