RNAIII-inhibiting peptide and/or nisin inhibit experimental vascular graft infection with methicillin-susceptible and methicillin-resistant Staphylococcus epidermidis

Objective. To investigate the efficacy of RNAIII-inhibiting peptide (RIP) and nisin as prophylactic agents in a rat model of vascular graft infection. Design. Prospective, randomized, controlled animal study. Materials. Two hundred and twenty adult male Wistar rats. Staphylococcus epidermidis ATCC 12228 and one clinical isolate of methicillin-resistant S. epidermidis. Drugs: RIP nisin and rifampin. Methods. Graft infections were established in the dorsal subcutaneous tissue by implantation of 1 cm 2 sterile Dacron grafts, followed by topical bacterial inoculation: grafts were retrieved at 7 days. The study included a control group (without inoculation) and two series composed of five groups for each staphylococcal strain: one contaminated group that did not receive any antibiotic prophylaxis, three contaminated groups that received grafts soaked with 10 mg/l RIP, 10 mg/l nisin, 10 mg/l rifampin, or RIP + nisin. The main outcome measure was the extent of bacterial at graft harvest. Results. The bacterial counts for methicillin-resistant S. epidermidis on explanted grafts were 6.1 +/- 2.8 x 10(2) 7.8 +/- 3.0 x 10(3) and 5.5 +/- 2.9 x 10(4) for RIP, nisin and rifampin, respectively. RIP and nisin used in combination reduced the bacterial count to < 10. The results for S. epidermidis were similar. Conclusions. RIP and nisin could be used in combination to coat medical devices to prevent drug resistant S. epidermidis infections.