Does in situ replacement of a staphylococcal infected vascular graft with a rifampicin impregnated gelatin sealed Dacron graft reduce the incidence of subsequent infection?

Background. The aim of this study was to treat methicillin-resistant Staphylococcus aureus (MRSA) or S. epidermidis prosthetic vascular graft infections by in situ replacement with a rifampicin bonded Gelsoft graft. Methods. Interposition grafts were placed in the internal carotid artery of 56 merino sheep and the graft surface directly inoculated with 10(8) colony forming units (CFU) of MRSA (29) or S. epidermidis (27). At three weeks, grafts were harvested and sheep allocated to three groups. In the MRSA infected group, sheep received grafts soaked in 1.2 mg/ml (12), 10 mg/ml (10) and no (7) rifampicin. For S. epidermidis, sheep received grafts soaked in 1.2 mg/ml (10), 10 mg/ml (9) and no (8) rifampicin. There were two deaths, in the MRSA study group, one each from the rifampicin treated groups. The remaining sheep were euthanased and grafts harvested three weeks following regrafting. Grafts at harvests were assessed for perigraft abscess formation, anastomotic disruption and graft thrombosis. Swabs were taken to assess bacterial growth in the perigraft tissues, and external and internal graft surfaces. A 3-5 mm segment of graft was incubated in a broth medium. For S. epidermidis the remainder of the graft was ground and then incubated in a broth medium. Results. For MRSA, no statistical difference between the groups was reached for any of the measured parameters. For S. epidermidis, a significant reduction was reached for total infected specimens in the 10 mg/ml group compared to both control (p<0.001) and 1.2 mg/ml (p<0.005) groups. Graft reinfection was also less likely to occur with S. epidermidis than MRSA. Conclusions. In conclusion, replacement of S. epidermidis infected vascular grafts with 10 mg/ml rifampicin soaked Gelsoft graft is effective in reducing subsequent S. epidermidis infection. This conclusion cannot be extended to MRSA infected vascular grafts.