Staphylococcus epidermidis is an increasingly recognized causative organism of vascular graft infections. To increase our understanding of this problem we have tried to establish Staph. epidermidis vascular graft infection in sheep by direct inoculation.
A 2 cm long, 5 mm diameter polytetrafluoroethylene (PTFE) or a gelatin sealed Dacron vascular graft was inserted into the left carotid artery, At the completion of the operation 1 mL of normal saline containing either 104, 106, or 108 colony forming units (cfu) of a slime producing Staph. epidermidis was inoculated directly onto the graft. After 3 weeks the grafts were harvested in a sterile fashion. Swabs were taken of the perigraft tissues and the external and internal aspects of the grafts; a 3–5 mm segment of the graft was incubated in broth medium and a second segment was ground for 5 min and then incubated in broth medium. Note was made of the presence of abscess formation, anastomotic failure or thrombosis.
Thirteen sheep received a PTFE graft and 14 received a gelatin sealed Dacron graft. Three sheep died immediately postoperatively. The rate of infection was 40% at 104. 67% at 106 and 80% at 108 cfu Staph. epidermidis. In only four cases were all five cultures positive. In nine cases two or less cultures were positive, the majority of these being the broth cultures. Nine other organisms were isolated from nine mixed infections. Nine out of 13 PTFE and seven out of 11 Dacron grafts were infected.
The rate of graft infection grew with increasing concentration of inoculum. Retrieval of bacteria was greatest when the graft was cultured directly, especially with physical disruption. Infection with additional organisms was common. There was no difference in the infection rate between gelatin sealed Dacron and PTFE.
