Experimental prophylaxis of Staphylococcus aureus endophthalmitis after vitrectomy -: The use of antibiotics in irrigating solution

Purpose: To test the efficacy of clindamycin and gentamicin in irrigating solution during vitrectomy to prevent experimental Staphylococcus aureus endophthalmitis. Materials and Methods: Thirty-six New Zealand white rabbits were divided into six groups. Vitrectomy using two different irrigating solutions was followed by intravitreal injection of S. aureus: Group 1, balanced salt solution (BSS) followed by 1,000 colony-forming units (CFU) S. aureus; Group 2, BSS fortified with clindamycin, 10 mug/mL, and gentamicin, 8 mug/mL (CGBSS), followed by intravitreal injection of 1,000 CFU S. aureus; Group 3, BSS followed by 2,000 CFU S. aureus; Group 4, CGBSS followed by 2,000 CFU S. aureus; Group 5, BSS followed by 4,000 CFU S. aureus; and Group 6, CGBSS followed by 4,000 CFU S. aureus. The eyes were examined clinically after surgery. Vitreous samples were cultured and histologic studies were performed. Results: Severe endophthalmitis developed in all eyes in Groups 1, 3, and 5 (not given antibiotics). No endophthalmitis developed in Group 2. In Group 4, five of the six eyes were normal and one eye had endophthalmitis. In Group 6, one eye had clear vitreous and fundus, three eyes had moderate vitreous haze, and the other four eyes demonstrated severe endophthalmitis. Bacterial growth in Groups 1,2, 3, 4, 5, and 6 were 4/4, 0/4, 6/6, 1/6, 4/6, and 2/8 eyes, respectively. Conclusion: When 1,000 to 2,000 CFU S. aureus were injected after vitrectomy, clindamycin and gentamicin in the irrigating solution significantly diminished the intraocular inflammation and the rate of positive bacterial culture. Clindamycin and gentamicin in the irrigating solution were not significantly effective when 4,000 CFU bacteria was injected; however, the degree of inflammation was less severe than in the control group.