Graft Infectivity of Rifampin and Silver-Bonded Polyester Grafts to MRSA Contamination

Abstract

The purpose of this study was to evaluate the ability of vascular polyester grafts with antibacterial properties to resist colonization following surface contamination by methicillin-resistant Staphylococcus aureus(MRSA) in an experimental canine model or aortic graft infection. Twenty-four pathogen-free dogs underwent replacement of the infrarenal aorta with either a rifampin-soaked (30 mg/mL) or silver-impregnated (Ag-acetate) woven polyester graft. Following implantation, the external graft surface was inoculated with 2 mL of 107 colonyforming units/mL (CFU) of MRSA. Preoperative antibiotic prophylaxis consisted of a single intravenous dose of 500 mg of sodium cefazolin. Four grafts of each type were explanted at 3, 7, and 14 days after implantation. Quantitative cultures (CFU/specimen) of perigraft fluid (1 mL), graft material (1 cm segment), and adjacent aorta (1 cm segment) were performed. Differences between grafts are expressed as% mean log reduction in recoverable CFU compared to the inoculation solution concentration of 107 CFUs. At 3 days, explanted rifampinsoaked grafts exhibited no MRSA growth (4 of 4 grafts) and a =97% mean log reduction of MRSA CFUs from the adjacent aorta and perigraft fluid (PGF). At 3 days, all silver-bonded grafts exhibited signs of infection and a mean log CFU reduction of MRSA ranging from 68% (absolute range 101–103 recoverable CFU) for the graft, 79% (absolute range 101–103 recoverable CFU) for the aorta, and 86% (absolute range 101–104 recoverable CFU) for PGF. The 7-day rifampin group had an average log reduction in MRSA CFU of 72% (graft), 58% (PGF), 75% (aorta). Quantitative cultures of 14-day rifampin grafted demonstrated continued bacterial growth suppression with mean MRSA CFU log reductions of 82%, graft; 72%, PGF; 89%, aorta. Silver-bonded grafts demonstrated <50% mean CFU reduction in MRSA growth at 7 days (absolute range 105–107 recoverable CFU) and 14 days (absolute range 103–107 recoverable CFU). No animal died from sepsis or anastomotic hemorrhage. Neither rifampin nor silverbonded grafts demonstrated prolonged resistance to surface MRSA contamination. Rifampinsoaked polyester grafts exhibited a marked but transient resistance MRSA colonization likely the result of high antibiotic concentration in the perigraft tissue. While both types of grafts failed to eradicate the MRSA infection future research with silver-bonded grafts that have an additional antibiotic attached may have a place in the treatment of MRSA infection.