The most common bacterial etiologic agent in keratitis associated with contaminated contact lens cleaning solutions is which organism?

• A. Chryseobacterium meningosepticum
• B. Pseudomonas aeruginosa
• C. Francisella tularensis
• D. Escherichia coli

Answer: (B)

The scenario tests why a moist, environmental bacterium becomes the typical culprit in keratitis linked to contaminated contact lens solutions. Pseudomonas aeruginosa thrives in aqueous, dirty, or moist environments and readily adheres to contact lenses, where it can form resilient biofilms that resist disinfection. Once on the cornea, it is highly virulent, promoting rapid inflammation and tissue damage that can lead to ulcers if not treated quickly. This combination—environmental abundance in moisture, strong lens-adherence/biofilm formation, and aggressive corneal damage—explains why it is the most common cause of lens-associated keratitis.

Other organisms listed may cause ocular infections but are much less commonly implicated in this specific setting. Chryseobacterium meningosepticum can cause keratitis, but far less often than Pseudomonas in contact lens–related cases. Francisella tularensis is a rare zoonotic pathogen with little association to lens-related keratitis. Escherichia coli is primarily an enteric organism and is not a usual cause of keratitis from contact lens solutions.