Bacterial conjunctivitis. Computer artwork of bacteria (green, not to scale) on the surface of a bloodshot eye (red blood vessels). Acute bacterial conjunctivitis is an inflammation of the conjunctiva, the delicate mucous membrane covering the front of the eye and the insides of the eyelids. The conjunctiva becomes red and swollen, and may discharge water or pus. Conjunctivitis can be caused by bacterial infection, a virus, an allergy, or by physical or chemical irritants. Bacterial infections respond to antibiotic eye drops. Uncomplicated conjunctivitis is generally not serious and does not usually affect vision.