Listeria monocytogenes keratitis.

We treated a farmer who had Listeria monocytogenes bacterial keratitis. Therapy with topical antibiotics was unsuccessful; it was necessary to treat the patient with topical and systemic penicillin and gentamicin. To elucidate the pathogenesis of this infection, we developed a rabbit model. Using the patient's strain of L. monocytogenes, we determined that the severity of the rabbit infection was dose-related. If we used an inoculum of more than 10(7) organisms, many of the features of the human Listeria keratitis were mimicked. We also found that treatment with either penicillin or gentamicin did not control the infection as well as using both antibiotics simultaneously, a combination which resulted in relatively rapid resolution of infection and no corneal scarring. The human and animal data indicate that L. monocytogenes can be a virulent corneal pathogen. Listeria corneal infections must be treated aggressively with both penicillin and gentamicin to prevent permanent visual loss.