Bacterial infections of the eye most commonly result in inflammation of the conjunctiva—conjunctivitis—or inflammation of the cornea—keratitis. Staphylococcus epidermidis and Pseudomonas aeruginosa are the most common bacterial causes of keratitis. These organisms adhere to the surface of contact lenses, providing close contact with the eye surface for colonization and increasing the risk of keratitis in contact lens users. Proper cleaning and care (including removing before sleep) of lenses greatly reduces the risk. Both P. aeruginosa and S. epidermidis are identifiable through culturing, immunoassay, or polymerase chain reaction tests. Prompt treatment of keratitis is necessary to avoid complications that can lead to blindness. Treatment with fluoroquinolone or other antibiotic eye drops is necessary. Care needs to be taken in antibiotic selection, though, since strains of both P. aeruginosa and S. epidermidis may carry antibiotic resistance genes to one or several common first-line antibiotics.Neisseria gonorrhoeae causes the sexually transmitted disease gonorrhea. Gonorrhea is a sexually transmitted disease caused by a gonococcus, the gram-negative bacterium Neisseria gonorrhoeae, which frequently infects both males and females, but often shows no symptoms in females. It enters the body through mucous membranes of the urogenital system, as well as the mouth and throat. If it invades the delicate tissue of the eye it can be pathogenic. This conjunctivitis has an explosive onset, progressing rapidly over several hours. The eye is severely inflamed, with copious mucous discharge, eyelid swelling, and corneal melting leading to perforation. N. gonorrhoeae is particularly virulent because it is one of the few bacteria (others include N. meningitidis, C. diphtheriae, Shigella species, Haemophilus influenzae biotype III, and Listeria monocytogenes) that can penetrate a healthy, intact cornea. N. gonorrhoeae adheres rapidly to the corneal surface with hair-like pili surface appendages and is enveloped in the corneal epithelial cells. The bacterium then releases proteases that lyse, or break down, the corneal cells and activate native corneal matrix-derived metalloproteinases (MMPs) that trigger autodigestion, and this leads to corneal perforation. Treatment requires systemic therapy in the form of a third-generation cephalosporin such as ceftriaxone or spectinomycin (for those with a penicillin allergy). Erythromycin or gentamicin ointment is also recommended for topical therapy.