Experimental postoperative endophthalmitis

Various inocula of vancomycin-sensitive E faecalis (EF01), S aureus (SA02), S epidermidis (SE03), and B cereus (BC04), were intravitreally inoculated into an aphakic rabbit model with and without vancomycin, with or without vitrectomy. A summation average of the clinical response mean scores of various inocula (10(3), 10(5), 10(7) cfu) in the absence of therapy ranked these etiologic agents in the order of severity as SE03 (1.4), BC04 (1.8), EF01 (2.3), and SA02 (2.8). These favorably compared with the histopathology cavitary/noncavitary mean scores in increasing order of severity: SE03 (1.7/0.6), BC04 (1.7/0.9), EF01 (2.4/1.1), and SA02 (2.5/1.5), compared with control eyes (1.1/0.4). If the inoculum was increased to 10(7) cfu, SE03 (2.4/0.9) and BC04 (2.8/2.0) could equate EF01 and SA02. Treatment with 1 mg of vancomycin, with or without vitrectomy, did not significantly alter the overall inflammatory response to these four endophthalmitis isolates. No treatment was necessary to achieve > 99.9% killing effect by 72 hours when testing BC04, while any of the treatment modalities during 72 hours achieved 99.9% killing effect when testing SE03. No treatment modality achieved a 99.9% killing effect when testing EF01 or SA02. No single in vitro result could predict the in vivo microbiologic behavior of this model. Further research is needed to better understand the role of antiinflammatory agents, multiple drug therapy, and multiple-injection single-drug therapy with or without vitrectomy, and their impact on the inflammatory response in the aphakic model, to better treat endophthalmitis and thus improve visual prognosis.