Which coagulase-positive Staphylococcus is a frequent cause of keratitis in contact lens wearers?

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

Answer: (A)

Coagulase status helps distinguish Staphylococcus species, and the coagulase-positive member commonly linked to keratitis in contact lens wearers is Staphylococcus aureus. This organism can adhere to contact lenses and damaged corneal epithelium, form biofilms, and produce virulence factors such as toxins and protein A that promote tissue invasion and evasion of host defenses. The alternative Staphylococcus listed, epidermidis, is coagulase-negative, so it doesn’t fit the clue. Streptococcus pyogenes isn’t a Staphylococcus at all, and Pseudomonas aeruginosa, while a frequent cause of lens-related keratitis, is not a Staphylococcus. Thus Staphylococcus aureus best fits the question’s focus on a coagulase-positive Staphylococcus.