Which Gram-negative rod is most associated with contact lens–related keratitis?

• A. Pseudomonas aeruginosa
• B. Haemophilus influenzae
• C. Moraxella catarrhalis
• D. Escherichia coli

Answer: (C)

Pseudomonas aeruginosa is the organism most associated with contact lens–related keratitis because it thrives in moist environments and readily adheres to contact lenses, where it can form biofilms that resist disinfection. Its virulence allows it to invade corneal tissues quickly, leading to a rapidly progressive keratitis and risk of corneal ulcers if not treated promptly. The other organisms listed are less typical: Moraxella catarrhalis is a Gram-negative diplococcus not a rod and is more often linked to sinus or respiratory infections; Haemophilus influenzae is a small Gram-negative coccobacillus that can cause conjunctivitis but is not the classic cause of lens-related keratitis; Escherichia coli is primarily a GI tract organism with ocular infections far less commonly linked to contact lens wear. The combination of lens adherence, biofilm formation, and the moist lens environment makes Pseudomonas aeruginosa the classic culprit for this condition.