Contribution of secreted proteases to the pathogenesis of postoperative Enterococcus faecalis endophthalmitis

PURPOSE: To determine how a secreted protease contributes to the pathogenesis of post-cataract endophthalmitis caused by Enterococcus faecalis using an aphakic rabbit endophthalmitis model. SETTING: Department of Ophthalmology, Ehime University School of Medicine, Ehime, Japan. METHODS: The pathogenesis of E faecalis OG1S (secreted protease-positive) and E faecalis OG1X (secreted protease-negative derivative of OG1S) was compared. After lens removal by phacoemulsification, either strain was inoculated into the lens bag. Changes in bacterial growth, electroretinography (ERG), and pathology of eyes were comparatively monitored throughout the course of the infection. Alternatively, culture fluid from either strain was injected into the vitreous body and ERG and pathology of the eyes were also examined. RESULTS: The levels of growth in the anterior chamber and vitreous cavity were similar for both strains. However, infection with OG1S resulted in a significantly greater reduction in ERG b-wave amplitude than OG1X. Histological examination showed that the posterior lens capsules were severely affected in eyes infected with OG1S, and inflammatory cells and cocci were found in the anterior vitreous cavity 24 hours after the infection. By 48 hours, the retina architecture was profoundly affected in eyes infected with OG1S. In contrast, few pathological changes were noted in the posterior lens capsules and retina of eyes infected with OG1X. Culture fluid in which OG1S had grown decreased ERG b-wave amplitude and caused morphological changes of the posterior capsule and retina similar to those in the infected eye. CONCLUSION: An extracellular protease plays a major role in the pathogenesis of E faecalis-induced postoperative endophthalmitis.