The liquid form of sodium fluorescein is very susceptible to contamination by which organism?

• A. Pseudomonas aeruginosa
• B. Staphylococcus aureus
• C. Streptococcus pneumoniae
• D. Escherichia coli

Answer: (A)

Contamination risk in sterile ocular solutions often comes from organisms that thrive in moist, nutrient-poor environments and can readily colonize plastic containers. Pseudomonas aeruginosa fits that pattern best for liquid fluorescein: it grows well in aqueous solutions, forms biofilms on bottle surfaces, and is notably resistant to some preservatives, allowing it to proliferate even in small amounts of residue. This makes it the most likely contaminant of the fluorescein liquid. The other organisms listed are less commonly associated with contaminating sterile eye drops; they can cause infections but are not the typical culprits in this context.