ABSTRACT
Knowledge concerning human diseases caused by bacteria has been accumulating at an extraordinary rate since bacteria were first discovered nearly 175 years ago. This, however, is a minuscule fraction of the 3.5 billion years that bacteria have inhabited the earth and learned to adapt to their environment. The prokaryotic genome with its ability to acquire new DNA and rearrange existing genes gives bacteria an effective mechanism by which to colonize the vast number of ecological niches that exist on earth. The eye, like other body surfaces, is constantly exposed to bacteria, yet only a small proportion ever causes disease. In an idealized setting, bacteria and the human host would co-exist in a symbiotic relationship. In reality, however, co-existence is limited by either increased bacterial virulence or lapses in host defenses that result in infection.
