Which pathogens commonly cause cellulitis?

• A. Escherichia coli alone
• B. Fungal organisms
• C. Staphylococcus aureus and Streptococcus species
• D. Viruses

Answer: (C)

Cellulitis is a bacterial infection of the skin and underlying soft tissue that most often arises after a break in the skin, allowing bacteria from the surface to invade. The usual culprits are Staphylococcus aureus and Streptococcus species, because these skin-residing bacteria readily invade damaged skin and produce the rapid, spreading inflammation that characterizes cellulitis. This combination captures the two most common causes of acute bacterial skin infections and informs typical treatment choices that cover both organisms.

Escherichia coli isn’t the typical agent of uncomplicated cellulitis; it’s more commonly linked to infections arising from the gut or urinary tract and is less likely to be the sole cause in a standard skin/soft-tissue infection. Fungal organisms can cause skin infections, but they generally present differently and don’t cause the classic acute bacterial cellulitis pattern. Viruses don’t usually lead to cellulitis in the way bacteria do.