Prophylaxis against Staphylococcus epidermidis vascular graft infection with rifampicin-soaked, gelatin-sealed Dacron.

An animal model was used to assess the efficacy of rifampicin-impregnated, gelatin-sealed Dacron in the prevention of vascular graft infections caused by Staphylococcus epidermidis. Under a general anaesthetic an interposition graft was placed into sheep carotid artery. On completion of the operation 1 ml of normal saline containing 10(8) colony forming units (cfu) of a slime-producing S. epidermidis was inoculated directly onto the graft. After 3 weeks the graft was harvested. Swabs were taken of perigraft tissues, and of external and internal aspects of the graft. A 3-5-mm segment of the graft was incubated in broth medium and a second segment was ground for 5 min and incubated in broth medium. The presence of abscess formation and anastomotic disruption was assessed. Ten sheep received a gelatin-sealed Dacron graft (control), while nine received the same graft impregnated with rifampicin at a concentration of 1.2 mg/ml (treated). Eight of 10 control grafts were infected, with 30 of 50 possible cultures positive, compared with four of nine treatment grafts infected (P = 0.13) and 13 of 45 cultures positive (P = 0.004). The control group had four abscesses and two anastomotic disruptions; the treatment group had no abscesses (P = 0.05) or anastomotic disruptions (P = 0.26). Other organisms were isolated from nine of the 12 infected grafts, most commonly Staphylococcus aureus. There was no development of resistance to rifampicin. Rifampicin-impregnated, gelatin-sealed Dacron is successful at reducing the incidence of S. epidermidis vascular graft infection.

Development of a Staphylococcus epidermidis vascular graft infection model in sheep.

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 10(4), 10(6), or 10(8) 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 10(4), 67% at 10(6) and 80% at 10(8) 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.(ABSTRACT TRUNCATED AT 250 WORDS)

Assessment of abdominal aortic aneurysm with magnetic resonance imaging.

Pre-operative imaging of abdominal aortic aneurysms (AAA) is important in determining suitability for operation and operative approach. Ultrasound imaging is an excellent screening modality but is relatively poor at identifying renal arteries and the extent of iliac involvement. Computed tomography scanning with intravenous contrast and arteriography are invasive modalities that are associated with a small risk. Magnetic resonance imaging (MRI) offers the potential of accurate anatomical definition without use of contrast agents and passage of an intra-arterial catheter. Eight patients who had their AAA evaluated with MRI are reported. All had renal arteries accurately defined, intra-aneurysmal thrombosis was well delineated, and iliac extension was correctly identified in four cases. The initial experience has been most encouraging and the authors consider that MRI may become the investigation of choice for pre-operative AAA assessment.

Rifampicin impregnated Dacron grafts: no development of rifampicin resistance in an animal model.

AIM: Rifampicin impregnated Dacron grafts have been shown to be effective at preventing vascular graft infection in different animal models. The development of resistance to rifampicin would be a major drawback to the widespread use of such a graft. We aimed to determine how readily this would occur by using a sheep animal model. METHODS: Under general anaesthetic a 2cm long, 5mm diameter Dacron interposition graft inpregnated with 1.2 mg/ml rifampicin was placed in the left carotid artery. An extreme challenge of methicillin resistant Staphylococcus aureus (MRSA) using an inoculum of 10(9) colony forming units was placed directly onto the graft. The grafts were harvested at 3 weeks and cultures of the graft and tissues were taken. The presence or absence of any abscess formation, anastomotic disruption and graft thrombosis was noted. Any positive growths were identified and if found to be the same as the inoculum, the bacteria were used as the inoculum for another sheep. This was repeated once more. Thus we started with three sheep initially and used a total of nine sheep. RESULTS: There were no deaths. All grafts were infected with the same MRSA strain, confirmed on phage typing. There were three abscess and one anastomotic disruption. Seven of the grafts were occluded. The minimal inhibitory concentration (MIC) of the infecting inoculum and the bacteria retrieved were determined using the agar dilutional method. The MIC for the three initial inocula was < 0.007 mg/l. All subsequent strains isolated had an MIC of < 0.015 mg/l. This was a difference of one dilution and not significant. CONCLUSION: There was no development of rifampicin resistance using this animal model.

Comparison of fluoropolymer passivated Dacron and polytetrafluoroethylene grafts in a sheep model.

The search for an optimal prosthetic vascular graft suitable for small vessels continues. The aim of this study was to compare a fluoropolymer passivated Dacron graft with a standard polytetrafluoroethylene graft. A sheep animal model was used. Under general anaesthesia a 5-cm length of 5-mm diameter graft was interposed into the left carotid artery. After an interval of 1, 2 or 3 months the sheep were reanaesthetized and a carotid angiogram performed before harvesting the graft. Graft patency was assessed by macroscopic inspection, angiography and histological examination. Overall, four of eight polytetrafluoroethylene grafts and three of ten fluoropolymer passivated Dacron grafts remained patent with similar patency rates at 1, 2 and 3 months. Histological examination of all available grafts showed evidence of fibrointimal hyperplasia. All but one of the occluded grafts had fibrointimal hyperplasia.