Bacterial adherence to synthetic vascular prostheses and influence of human plasma. An in vitro study

In Situ Graft Replacement for a Ruptured Abdominal Aortic Aneurysm Infected with Listeria monocytogenes after Endovascular Aneurysm Repair

Listeria monocytogenes infection and rupture of the aneurysm sac, after endovascular aneurysm repair (EVAR), are both rare. We report the case of an 82-year-old man who presented with a ruptured aneurysm by infection with L. monocytogenes after EVAR. We successfully treated him by in situ reconstruction with a bifurcated expanded polytetrafluoroethylene (ePTFE) graft, with partial removal of the infected stent graft. At 30 months from the reoperation, the patient was in good health at home, with no symptoms of infection, and the gallium-67-citrate single-photon emission computed tomography/computed tomography (SPECT/CT) fusion images confirmed no fluid accumulation.

The management of aortic stent-graft infection: endograft removal versus conservative treatment

BACKGROUND

Aortic stent-graft infections (ASGIs) are associated with significant mortality. We report our experience of two cases of ASGI treated differently and successfully.

METHODS

Two patients presented with constitutional symptoms some months after scheduled endovascular repair of aortic aneurysm (EVAR). Patient 1 had an abscess formation around the endograft in continuity with the right groin. Due to patient comorbidities, a conservative treatment was performed. Patient 2 had an abscess formation with air surrounding the stent graft. The patient was treated successfully by endograft removal.

RESULTS

Computed tomographic scan follow-up at 6 months from surgery showed no evidence of recurrent infection.

CONCLUSION

Despite the recommended treatment of ASGI being surgery, conservative treatment can be performed successfully in patients with high surgical risk, avoiding aortic clamping. We present the first reported case of ASGI due to Streptococcus haemolyticus, the second case due to a fungus, and the second reported case of spondylodiscitis after EVAR.

Local Infections After Above-Knee Prosthetic Femoropopliteal Bypass for Intermittent Claudication

BACKGROUND

The use of prosthetic grafts in the treatment of intermittent claudication is still a controversy. Prosthetic bypass for this usually benign condition may in some cases lead to a graft infection. This potentially disastrous complication is difficult to manage.

METHODS

One hundred forty-one consecutive operations done on 129 patients between January, 1990 and December, 2001 in a single university vascular unit have been studied. Lymphatic complications and local infections have been related to preoperative risk factors, complications, secondary procedures, and outcome.

RESULTS

During a mean follow-up period of 42 months, lymph complications occurred after 18 operations, surgical site infection after 11 procedures, and graft infection after 17 operations. Eleven infected grafts were treated successfully without graft excision. Six of these grafts healed with antibiotics only. The risk of developing a local infection was significantly correlated with postoperative lymph fistula. Reoperative surgery was associated with graft infection. Graft infection caused by Staphylococcus aureus always warranted surgery, either local revision or graft excision.

CONCLUSIONS

The present series had a high frequency of graft infections. Our data suggest that a selective approach should be taken towards excision of infected femoropopliteal prostheses. The need for and extent of surgery should be individualized according to the clinical presentation of the graft infection and the type of bacteria involved. We advocate a conservative attitude towards surgical treatment of intermittent claudication.

Optimization of the resistance of arterial allografts to infection: comparative study with synthetic prostheses

Arterial allografts can be used for in situ treatment of prosthetic graft infection. The purpose of this in vitro study was to compare the resistance of allografts and synthetic prostheses to infection by five strains of bacteria and to study antibiotic treatments designed to reduce allograft infection. Fresh and cryopreserved allografts were compared with synthetic prostheses made of various biomaterials including PTFE, plain Dacron, gelatine-sealed Dacron, and gelatine-sealed, rifampicine-bonded Dacron. Allografts were used with or without treatment using an antibiotic containing gentamycine, lincomycine, and vancomycine. The bacterial strains tested were Escherichia coli, Staphylococcus aureus, slime-producing Staphylococcus epidermidis, non-slime-producing Staphylococcus epidermidis, and Pseudomonas aeruginosa. Infection was evaluated by counting the number of adherent bacteria on the allograft or synthetic material after rinsing and ultrasonication. Statistical analysis was achieved using nonparametric Mann-Whitney tests. Results showed that allografts not treated with antibiotics were highly susceptible to bacterial infection. Antibiotic treatment decreased infection. Application of antibiotic after thawing cryopreserved allografts led to a significant decrease. None of the biomaterials tested provided sufficient protection against bacteria resistant to the antibiotics used.

Exposure of plasma proteins on Dacron and ePTFE vascular graft material in a perfusion model

OBJECTIVES

to compare the exposure of plasma proteins adsorbed onto three vascular graft materials (polytetrafluoroethylene ePTFE and two modifications of polyethyleneterephthalate Dacron).

METHODS

surface exposure of fibronectin, vitronectin, thrombospondin, antithrombin III, IgG, high molecular-weight kininogen, fibrinogen, albumin and plasminogen was studied by incubation with radiolabelled antibodies in a perfusion model. Perfusion times with human plasma were 1, 4, 24 and 48 hours.

RESULTS

all proteins could be detected at 1, 4, 24 and 48 hours after the start of perfusion. Overall, the least amount of proteins adsorbed onto ePTFE.

CONCLUSIONS

the low adsorption of proteins onto ePTFE may be one of the reasons for the lower incidence of infections reported with this material.

Patch incorporation in diaphragmatic hernia

BACKGROUND/PURPOSE

Biomaterial insertion often is required for closure of congenital diaphragmatic hernia (CDH). The optimal biomaterial remains uncertain. This study was designed to compare a commonly used patch (polytetrafluoroethylene) with a recently available fabric, fluorinated polyester. The aim of this study was to determine the clinical performance, histological tissue-polymer interaction, bacterial adhesion, and shrinkage rates of biomaterial inserted endoscopically into a CDH lamb model.

METHODS

Polytetrafluoro-ethylene (PTFE) and fluorinated polyester (FP) were randomised for laparoscopic patch insertion into 12 lambs. All lambs (age <4 weeks) underwent 3-port laparoscopy, surgical creation of diaphragmatic hernia, and sutured patch placement. Two PTFE and 2 FP lambs were killed at 1-, 3-, and 6-month intervals postoperatively. Postmortem examination histopathology, electron microscopy, and specific bacterial broth immersion (Escherichia coil, Staphylococcus aurens, and epidermidis) were performed.

RESULTS

All 12 lambs completed the study with intact patches that were fully peritonised. One abdominal adhesion was noted in a FP lamb at 6 months. FP was comparatively easier to insert, manipulate, and suture endoscopically. Histopathology findings showed that PTFE patches created a strong peripheral foreign body reaction with dystrophic calcification, whereas FP was well incorporated with intrapatch fibroblastic activity and neovascularsation. No significant difference in resistance to bacterial adhesion of relevant organisms was noted between the materials. Graft shrinkage for FP was 7% in one direction only, evident by 3 months.

CONCLUSIONS

Fluorinated polyester has advantages in this laparoscopic lamb model. It shows rapid and sustained incorporation with intrapatch neovascularisation when compared with polytetrafluoro-ethylene's significant foreign body reaction. It was preferred for its endoscopic handling and suturing properties. The laparoscopic techniques used may contribute to the general lack of adhesions, and insufficient data are available to comment on the comparative effect of the materials on adhesion formation. No difference was demonstrated in resistance to bacterial adherence in the harvested materials.

Influence of heparin coating on in vitro bacterial adherence to poly(vinyl chloride) segments

End-point attached, covalently bound heparin has been shown to be effective in preventing activation of the coagulation cascade by biomaterials. Data concerning its possible influence on bacterial attachment and resistance to biomaterial-associated infection are, so far, lacking. In the present work, the in vitro adherence of Staphylococcus aureus, Staphylococcus epidermidis and Escherichia coli, one isolate of each species, to plain poly(vinyl chloride) (plain PVC) and heparin coated poly(vinyl chloride) (EPA-PVC) segments was compared. Also, the influence of precoating the segments with human normal plasma for 2 h was studied. 35S-Methionine was used to radiolabel bacteria. The segments were exposed to bacterial suspensions of approximately 10(7) colony forming units (CFU) per milliliter at 37 degrees C for 0.5-6 h. Following repeated washing in phosphate buffered saline (PBS), radioactivity associated with the segments was measured. Plain PVC as compared to EPA-PVC bound significantly more cells of all three tested species. Plasma precoating significantly decreased adherence of the tested species to plain PVC but did not affect the binding to EPA-PVC. However, after precoating with human plasma, EPA-PVC compared to plain PVC showed a higher binding of S. aureus which might possibly be due to bridging effects of fibronectin or other plasma proteins, interacting with S. aureus.

Reduced susceptibility of polytetrafluoroethylene vascular prostheses to colonization by Staphylococcus aureus following in situ endothelialization

The impact of endothelialization of polytetrafluoroethylene (PTFE) grafts on susceptibility to experimental colonization by Staphylococcus aureus was studied in a rat model. One hundred and eight grafts (2 mm inner diameter, 5 mm length) were implanted into the infrarenal aorta (54 rats) or the infrarenal caval vein (54 rats). The progress of endothelialization following graft implantation was evaluated by SEM at 1, 3, 7, and 14 days on 6 grafts from each group. We found that the endothelialization was more rapid in caval vein than in aorta: The caval vein grafts were completely endothelialized 2 weeks following implantation compared with endothelialization of approximately 0.5 mm of aorta grafts, measured from each anastomosis. During this time, the resistance to standardized intravenous challenge with 10(8) colony-forming units of S. aureus increased gradually in both groups, and all caval vein grafts tested at 2 weeks were sterile. However, all aorta grafts challenged at 2 weeks were colonized, although to a somewhat lower degree than at earlier challenge. Resistance of PTFE grafts to colonization with S. aureus thus correlated to the degree of endothelialization.

Influence of some plasma proteins on in vitro bacterial adherence to PTFE and Dacron vascular prostheses

The in vitro adherence of Staphylococcus aureus, Staphylococcus epidermidis and Escherichia coli (one strain of each species) to commercially available, microporous polytetrafluoroethylene (PTFE) and woven Dacron vascular grafts before and after coating with human plasma was compared. Standard size segments of the materials were incubated with 35S-labeled bacteria for 0.5-18 h and, following washes, the radioactivity associated with the segment was measured. The binding of each of the tested species to native Dacron was higher than to PTFE. After coating with human plasma, however, the binding of all three species to PTFE was significantly enhanced, whereas the binding to Dacron was reduced. In addition, the influence of coating with serum albumin (HSA), immunoglobulin G (IgG), fibrinogen (Fg) or fibronectin (Fn) rather than whole plasma was tested. We found that coating with HSA reduced the binding of all three species to Dacron and of staphylococci to PTFE. IgG decreased the binding of S. epidermidis and E. coli to Dacron and of S. epidermidis to PTFE. In contrast, Fg enhanced the binding of S. aureus both to Dacron and PTFE, and that of E. coli to PTFE, but decreased the binding of S. epidermidis and E. coli to Dacron. Fn enhanced the binding of S. aureus to Dacron, and of E. coli to PTFE, but decreased the binding of S. aureus to PTFE and of S. epidermidis both to PTFE and Dacron. Thus, both whole plasma and some isolated plasma proteins were found to modulate bacterial adherence to two tested graft materials. From a clinical point of view, bacterial binding to plasma-coated rather than native materials may more adequately determine the likelihood of in vivo colonization of the various materials. Furthermore, precoating of materials with selected proteins may be of value in the prevention of graft colonization.