Bullous impetigo is most often caused by which organism?

• A. Staphylococcus aureus
• B. Group A Streptococcus
• C. Staphylococcus epidermidis
• D. Pseudomonas aeruginosa

Answer: (A)

Bullous impetigo is driven by toxin-producing Staphylococcus aureus. Strains of S. aureus release exfoliative toxins that act on desmoglein-1 in the superficial layers of the epidermis. This causes a targeted split in the skin just below the stratum granulosum, leading to flaccid bullae that drain and rupture easily, leaving the characteristic thin crusts. Because this toxin-mediated mechanism is specific to S. aureus, bullous impetigo is most often caused by this organism. Other organisms listed—group A Streptococcus, Staphylococcus epidermidis, and Pseudomonas aeruginosa—do not produce the same exfoliative toxin pattern that creates these localized bullae, so they are not the typical cause of bullous impetigo.