In postoperative ocular infections, which organism is most commonly isolated?

• A. Staphylococcus aureus
• B. Staphylococcus epidermidis
• C. Streptococcus pneumoniae
• D. Streptococcus pyogenes

Answer: (B)

Postoperative ocular infections are most often driven by organisms that live on the skin and eyelids and can colonize implanted materials. Staphylococcus epidermidis fits this pattern because it is a coagulase-negative staphylococcus that is part of the normal eyelid and conjunctival flora and has a strong tendency to adhere to intraocular lenses and other prosthetic devices. Its ability to form biofilms protects it from immune clearance and antibiotics, allowing infection to take hold after surgery. This combination of being common on the ocular surface and capable of persisting on implants makes Staphylococcus epidermidis the most frequently isolated organism in postoperative endophthalmitis. In contrast, Staphylococcus aureus and the Streptococcus species are less commonly involved in these postoperative ocular infections, though they can cause more acute and severe disease when they do occur.