The organism associated with a disease characterized by a pseudomembrane in the throat and an exotoxin absorbed into the bloodstream with lethal effect is which species?

• A. Arcanobacterium haemolyticum
• B. Staphylococcus aureus
• C. Streptococcus pyogenes
• D. Corynebacterium diphtheriae

Answer: (D)

Pseudomembranous pharyngitis with systemic, often lethal toxin effects is classic for diphtheria. The organism is Corynebacterium diphtheriae, a Gram-positive, non-spore-forming rod that produces diphtheria toxin. This toxin is an AB exotoxin that inactivates protein synthesis by ADP-ribosylating elongation factor-2, causing cell death and the characteristic grayish pseudomembrane in the throat. When the toxin enters the bloodstream, it can damage the heart and nerves, leading to myocarditis and neuropathies, which explains the lethal potential. The other organisms may cause pharyngitis or exudates, but they do not produce the diphtheria toxin or the classic pseudomembrane with systemic toxicity. Vaccination with diphtheria toxoid prevents this disease.