A child presents with a gray pseudomembrane on the tonsils and pharynx, accompanied by myocarditis and neuropathies. A Gram-positive bacterium isolated from the throat produces a toxin that inhibits protein synthesis by inactivating elongation factor-2 (EF-2). Which of the following organisms is the most likely cause?

The correct answer to the question "A child presents with a gray pseudomembrane on the tonsils and pharynx, accompanied by myocarditis and neuropathies. A Gram-positive bacterium isolated from the throat produces a toxin that inhibits protein synthesis by inactivating elongation factor-2 (EF-2). Which of the following organisms is the most likely cause?" is Option C: Corynebacterium diphtheriae.

The other options — A) Staphylococcus aureus, B) Streptococcus pyogenes, D) Clostridium botulinum — are incorrect for this USMLE Exam Prep question. As explained above: Corynebacterium diphtheriae produces diphtheria toxin, an exotoxin that inhibits host cell protein synthesis by ADP-ribosylating and inactivating elongation factor-2 (EF-2), leading to cell death and…