EVALUATION OF THERAPEUTIC MEASURES FOR TREATING ENDOPHTHALMITIS CAUSED BY ISOGENIC TOXIN-PRODUCING AND TOXIN-NONPRODUCING ENTEROCOCCUS-FAECALIS STRAINS

Purpose. Management of endophthalmitis typically includes antibiotic c ombinations to arrest bacterial growth and antiinflammatory agents to limit inflammatory damage to sensitive tissues. Little research has be en reported that systematically evaluates the contribution of each the rapeutic component for treating infections caused by organisms of vary ing virulence. The authors determined the relative value of the antiin flammatory corticosteroid, dexamethasone, as an intravitreal therapeut ic adjunct for the treatment of infection caused by either Enterococcu s faecalis expressing a cytolytic toxin preciously shown to contribute to the course and severity of infection, or an otherwise identical st rain of E. faecalis specifically attenuated in expression of the cytol ytic toxin. Methods. Endophthalmitis in rabbits was monitored using el ectroretinography (ERG). Eyes were infected with 100 colony forming un its of either the cytolytic or the noncytolytic E. faecalis strain, In travitreal ampicillin and gentamicin were administered at postinfectio n dq 1, and intravitreal dexamethasone was either omitted or administe red at day -1, 1, or 1.5. Results. ERG B-wave amplitude declined preci pitously throughout the course of infection with cytolytic toxin-produ cing E, faecalis, despite the administration of antibiotics and regard less of the time of dexamethasone administration. In fact, the ultimat e course of infection caused by cytolytic E. faecalis did not differ f rom the course in untreated controls. In contrast, infections caused b y specifically attenuated, noncytolytic strains of E. faecalis respond ed well to antibiotics augmented by antiinflammatory therapy when the latter was administered either 1 or 1.5 days after the initiation of i nfection. In these cases, no loss in ERG B-wave response was observed. Conclusions. These results underscore the importance of bacterial tox ins in infectious diseases of the eye and their contribution to treatm ent failures. These results further suggest that in cases of endophtha lmitis caused by toxin producing bacteria, significant improvement in clinical outcome win require specific therapeutic targeting of the tox ins involved.