Experimental colonization of an expanded polytetrafluoroethylene vascular graft with Staphylococcus aureus: A quantitative and morphologic study

Abstract

We developed an animal model to reproduce hematogenous seeding of vascular grafts with Staphylococcus aureus. Expanded polytetrafluoroethylene (ePTFE) grafts were implanted in 41 dogs as thoracoabdominal aortic bypasses for six durations of implantation between 2 hours and 6 months. The inoculum containing an average of 108 viable bacteria/ml was then injected intravenously in 1 minute. Normal dog aortas were used as controls. They entrapped very few bacteria (0.7 ± 1.7 colony-forming unit [CFU]/cm2). Colonization of ePTFE grafts was maximal after 2 hours of implantation (589 ± 733 CFU/cm2). Bacterial entrapment decreased after 2 days (225 ± 315 CFU/cm2, p < 0.001) and 8 days (70 ± 115 CFU/cm2, p < 0.001) of implantation, but it was similar after 8 days, 1 month (83 ± 90 CFU/cm2), or 6 months (93 ± 143 CFU/cm2) of implantation. Colonization of ePTFE measured after 2 months of implantation (371 ± 591 CFU/cm2) was significantly higher (p < 0.001) than after 1 or 6 months of implantation. More than 500 CFU/cm2 were seen in 37% of the prosthetic fragments tested after 2 hours of exposure to blood; 99% of the fragments tested after 6 months of implantation trapped less than 500 CFU/cm2. Scanning electron microscopy showed that staphylococci were mostly seen on native fibrin deposits, particularly after 2 hours and 2 months of implantation. That persistent susceptibility of a flow surface devoid of endothelium to hematogenous bacterial colonization has to be taken into account to prevent delayed graft infections. Furthermore, it would be important to compare the ePTFE with other types of grafts whose healing phenomena are different.