Which bacteria are most commonly implicated in keratitis?

• A. Streptococcus pneumoniae and Haemophilus influenzae
• B. Escherichia coli
• C. Staphylococcus epidermidis and Pseudomonas aeruginosa
• D. Neisseria meningitidis

Answer: (C)

Understanding keratitis involves recognizing which bacteria commonly invade the cornea, especially when the surface is damaged or exposed to lenses. Pseudomonas aeruginosa is a leading cause, particularly in contact lens wearers, because it thrives in moist environments around lenses and cases, and it can rapidly damage corneal tissue if not treated. Staphylococcus epidermidis is also a frequent offender; it’s a normal inhabitant of the ocular surface and eyelids, and it becomes a problem when the cornea is compromised, after surgery, or with lens use. Together, these two organisms are the most commonly implicated in keratitis, more so than the other bacteria listed, which are less typical causes in most settings.