Corynebacterium diptheriae

Categorization
Cell Wall: Gram Positive Shape: Rod, Non-sporulating
Metabolism: Facultative Anaerobe
Culture and Detection
  • Organism grows on Tellurite agar selective media, allowing detection from a nasopharyngeal swab.
Virulence Factors
  • Diptheria Toxin
    • Diptheria Toxin is an exotoxin that synthesized only by C. diptheriae that have undergone lysogenic transduction with a phage that contains the toxin gene. Diptheria Toxin is similar to a classic A-B Toxin.
    • The B Subunit binds to host cells and induces internalization of the toxin
    • The A Subunit is the toxic subunit and binds a ribosomal Elongation Factor, thus inhibiting protien translation, eventually leading to cell death.
Transmission
  • Is transmitted in aerosolized droplets between humans which are its only hosts.
Clinical Consequences
  • Pharyngeal Infection
    • C. diptheriae first colonizes and infects the pharynx causing necrosis of mucosal epithelial cells. This can be observed as an ulceration covered by a greyish/blackish "Pseudomembrane" composed of dead epithelial cells, dead neutrophils, and fibrin.
  • Complications
    • Toxin produced by pharyngeal C. diptheriae can then enter the blood stream, be spread systemically, and damage a variety of organs. Damage to the heart can result in a myocarditis while damage to peripheral nerves can cause peripheral neuropathy.
Incidence
  • Historically, Diptheria was mostly observed in children.
Prevention
  • DPT vaccine: One component of this vaccine (DPT) is the inactivated, formalin-fixed Diptheria Toxin which results in humoral immunity and thus inactivating antibodies to the toxin.
Treatment
  • Antitoxin: An antibody which binds Diptheria Toxin and is very effective
  • Antibiotics: Mostly used to prevent transmission and are not useful for preventing symptomology once it has arisen. Penicillin G or erythromycin are commonly used.