Enterococcus faecalis, a common cause of endophthalmitis after cataract surgery, is also associated with substantial loss of vision. The endophthalmitis vitrectomy study revealed that endophthalmitis caused by enterococci and streptococci was associated with the worst visual outcome. Several studies have examined the contribution of entero-coccal virulence factors to the pathogenesis of E. faecalis endophthalmitis. The cytolysin expressed by some strains of E. faecalis was shown to be a key determinant of the

Figure 3 Biofilm-producing Staphylococci.

Severity and treatability of enterococcal endophthalmitis. If enterococci were nontoxigenic, the infection responded well to treatment with effective antimicrobials in combination with dexamethasone. However, if the infection was caused by an identical organism additionally expressing the cytolysin, this therapeutic regimen was rendered completely ineffective.

Gelatinase and serine protease are secreted proteases that are regulated by a quorum-sensing system termed fsr; in addition, they have been reported to be associated with the retinal destruction. These proteases further have been shown to play a role in endophthalmitis of aphakic eye after cataract surgery. E. faecalis proteases may promote organism spread by penetrating the posterior lens capsule. Bacterial migration from the anterior chamber to the posterior chamber is a key event in the progression of endophthalmitis; in the posterior segment, severe retinal damage may result (Figure 4). A surface adhesin of E. faecalis, aggregation substance, contributes to altereD localization of the organism but otherwise appears to play a minor role.

In addition to these virulence traits, E. faecalis is intrinsically resistant to many antibiotics and is also capable of producing biofilm on IOL lens material. Both of these factors make infections with this organism very difficult to treat.

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