Purpose: To investigate the antibiotic susceptibility and clinical outcomes of endophthalmitis caused by methicillin-sensitive Staphylococcus aureus (MSSA) versus methicillin-resistant (MRSA) S. aureus. Design: Retrospective, consecutive case series. Methods: Charts of 32 patients with culture-proven S. aureus endophthalmitis seen at the Bascom Palmer Eye Institute from January 1, 1995, through January 1, 2008, were reviewed. Antibiotic susceptibility profiles, identified using standard microbiologic protocols, and visual acuity at 1 and 3 months were the main outcome measures. Results: MSSA was recovered from 19 (59%) of 32 patients and MRSA was recovered from 13 (41%) of 32 patients. Causes included cataract surgery in 18 (56%) of 32 patients, endogenous in 5 (16%) of 32 patients, bleb association in 4 (13%) of 32 patients, pars plana vitrectomy and ganciclovir implantation in 3 (9%) of 32 patients, and trauma in 2 (6%) of 32 patients. All isolates were sensitive to vancomycin. MSSA isolates were sensitive to all tested antibiotics, except one that exhibited fluoroquinolone resistance. In the MRSA group, frequent resistance occurred with the fourth-generation fluoroquinolones (moxifloxacin, 5 of 13 patients [38%]; gatifloxacin, 5 of 13 patients [38%]). The median presenting visual acuity was approximately hand movements for both MSSA and MRSA eyes. All eyes received intravitreal antibiotics. Pars plana vitrectomy was performed on 47% of MSSA and 61% of MRSA patients. A final visual acuity of 20/400 or better at 3 months was achieved in 59% of MSSA and 36% of MRSA patients (P = .5). Conclusions: Although all MSSA and MRSA isolates were sensitive to vancomycin, fewer than half of MRSA isolates were sensitive to the fourth-generation fluoroquinolones. Visual acuity outcomes between MRSA and MSSA eyes were not significantly different.
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