Prevention of Vascular Graft Infections with Antibiotic Graft Impregnation Prior to Implantation: In Vitro Comparison between Daptomycin, Rifampin and Nebacetin

Complications of e-PTFE Grafts in LDLT; Evaluation of Case Series

BACKGROUND

The expanded polytetrafluoroethylene (ePTFE) grafts are used to drain anterior sector veins during the living donor liver transplantation procedure. We aimed to analyze the potentially life-threatening complications, such as the infection and migration of ePTFE grafts.

METHODS

A total of 1264 liver transplantations (LTs) were performed for 1097 adult and 167 pediatric liver failure cases. In total, 1169 living and 95 cadaveric liver transplantation procedures were performed between 2011 and 2021. Right liver transplantation was performed in 1016 cases, including 1002 living donors and 14 cadaveric split right livers. Cadaveric LT was performed in 81 cases.

RESULTS

For 1002 right living liver grafts, 905 vascular grafts were used during the backtable for anterior sector outflow venoplasty. The most commonly drained segments were 5 and 8 (472 cases); there were isolated (5 or 8) and multiple drained segments. Vascular graft migration was described in 7 of 905 (0.77%) patients.

CONCLUSIONS

Although complication rates regarding ePTFE grafts are low, there are serious life-threatening causes of morbidity and mortality. We recommend cushioning the vascular graft with the omentum, which is effective in preventing graft migration.

A successful endovascular treatment of a patient with extended-spectrum beta-lactamase positive Escherichia coli related emphysematous distal abdominal aortitis rapidly progressing to a saccular aneursym

Infectious aortitis is a rare disease and associated with adverse clinical outcomes. A 66-year-old man was admitted to the emergency department with abdominal and lower back pain, fever, chills, and anorexia continuing for a week. A contrast-enhanced computed tomography (CT) scan of the abdomen showed multiple periaortic enlarged lymphatic nodes, mural wall thickening, and gas collections in the infrarenal aorta and proximal segment of right common iliac artery. The patient was hospitalized with the diagnosis of acute emphysematous aortitis. During hospitalization, extended-spectrum beta-lactamase-positive Escherichia coli was grown in all blood and urine cultures. Despite sensitive antibiotherapy, abdominal and back pain, inflammation biomarkers, and fever of the patient were not improved. Control CT demonstrated a newly developed mycotic aneurysm, increased intramural gas collection, and periaortic soft-tissue thickening. Urgent vascular surgery was recommended to the patient by the heart team, but the patient rejected surgery due to the high perioperative risk. Alternatively, an endovascular rifampin-impregnated stent-graft was successfully implanted and antibiotics were completed at 8 weeks. After procedure, inflammatory indicators were normalized and clinical symptoms of the patient were resolved. No microorganism grew on control blood and urine cultures. The patient was discharged with a good health.

Learning objective

Aortitis should be suspected in patients who present with fever, abdominal and back pain, especially in the presence of predisposing risk factors. Infectious aortitis (IA) accounts for a small part of all aortitis cases and the most common causative microorganism is Salmonella. The mainstay treatment of IA is sensitive antibiotherapy. Surgery may be required in patients who are unresponsive to antibiotics or develop aneurysm. Alternatively, endovascular treatment can be performed in selected cases.

Development of a dual-component infection-resistant arterial replacement for small-caliber reconstructions: A proof-of-concept study

Introduction: Synthetic vascular grafts perform poorly in small-caliber (<6mm) anastomoses, due to intimal hyperplasia and thrombosis, whereas homografts are associated with limited availability and immunogenicity, and bioprostheses are prone to aneurysmal degeneration and calcification. Infection is another important limitation with vascular grafting. This study developed a dual-component graft for small-caliber reconstructions, comprising a decellularized tibial artery scaffold and an antibiotic-releasing, electrospun polycaprolactone (PCL)/polyethylene glycol (PEG) blend sleeve. Methods: The study investigated the effect of nucleases, as part of the decellularization technique, and two sterilization methods (peracetic acid and γ-irradiation), on the scaffold's biological and biomechanical integrity. It also investigated the effect of different PCL/PEG ratios on the antimicrobial, biological and biomechanical properties of the sleeves. Tibial arteries were decellularized using Triton X-100 and sodium-dodecyl-sulfate. Results: The scaffolds retained the general native histoarchitecture and biomechanics but were depleted of glycosaminoglycans. Sterilization with peracetic acid depleted collagen IV and produced ultrastructural changes in the collagen and elastic fibers. The two PCL/PEG ratios used (150:50 and 100:50) demonstrated differences in the structural, biomechanical and antimicrobial properties of the sleeves. Differences in the antimicrobial activity were also found between sleeves fabricated with antibiotics supplemented in the electrospinning solution, and sleeves soaked in antibiotics. Discussion: The study demonstrated the feasibility of fabricating a dual-component small-caliber graft, comprising a scaffold with sufficient biological and biomechanical functionality, and an electrospun PCL/PEG sleeve with tailored biomechanics and antibiotic release.

Use of a Silver-Impregnated Vascular Graft: Single-Center Experience

INTRODUCTION

Vascular graft infection is a life threatening situation with significant morbidity and mortality. Bacterial graft infection can lead to false aneurysms, bleeding and sepsis. There are a lot of risky situations where grafts can become infected. It is therefore highly desirable to have a vascular graft that is resistant to infection. In this retrospective clinical study, a silver-impregnated vascular graft was evaluated in various indications.

METHODS

Our study included a total of 71 patients who received a silver-impregnated vascular graft during the period from 2013 to 2018. Patients had an aortoiliac localization of vascular graft in 61 cases (86%), and a peripheral localization on the lower limbs in 10 cases (14%). Indications for the use of these special vascular grafts were trophic lesions or gangrene in the lower limbs in 24 cases (34%), suspicious mycotic abdominal aortic aneurysm (mAAA) in 4 cases (5.5%), salmonela aortitis or aneurysms in 4 cases (5.5%), infection of the previous vascular graft in 11 cases (15.5%), other infections in 12 cases (17%), AAA rupture in 10 cases (14%) and other reasons (pre-transplant condition, multiple trauma, graft-enteric fistula) in 6 cases (8.5%). Thirty-day mortality, morbidity, the need for reintervention and amputation, primary and secondary graft patency, and finally the presence of a proven vascular graft infection were evaluated.

RESULTS

The 30-day mortality was 19.7%, and morbidity was 42.2%. The primary patency of the vascular graft was 91.5%. Reoperation was necessary in 10 cases (14%) and amputation was necessary in 10 cases (14%). The median length of hospital stay was 13 days and the mean follow-up period was 48 ± 9 months. During the follow-up period, six patients (8.5%) died from reasons unrelated to surgery or without any relation to the vascular graft. Secondary patency after one year was 88%. Infection of the silver graft was observed in three patients (4.2%).

CONCLUSIONS

Based on our results, the silver graft is a very suitable alternative for solving infectious, or potentially infectious, situations in vascular surgery. In particular, in urgent or acute cases, a silver graft is often the only option.

Treatment of vascular graft infections: gentamicin-coated ePTFE grafts reveals strong antibacterial properties in vitro

Vascular graft infections (VGI) are severe complications in prosthetic vascular surgery with an incidence ranging from 1 to 6%. In these cases, synthetic grafts are commonly used in combination with antimicrobial agents. Expanded polytetrafluoroethylene (ePTFE) is in clinical use as a synthetic graft material and shows promising results by influencing bacterial adhesion. However, the literature on antibiotic-bound ePTFE grafts is scarce. Gentamicin is a frequently used antibiotic for local treatment of surgical site infections, but has not been evaluated as antimicrobial agent on ePTFE grafts. In this study, we examine the antimicrobial efficacy and biocompatibility of novel types of gentamicin-coated ePTFE grafts in vitro. ePTFE grafts coated with gentamicin salt formulations with covalently-bound palmitate were evaluated in two drug concentrations (GP1.75% and GP3.5%). To investigate effects from types of formulations, also suspensions of gentamicin in palmitate as well as polylactide were used at comparable levels (GS + PA and GS + R203). Antibacterial efficacies were estimated by employing a zone of inhibition, growth inhibition and bacterial adhesion assay against Staphylococcus aureus (SA). Cytotoxicity was determined with murine fibroblasts according to the ISO standard 10993-5. Gentamicin-coated ePTFE grafts show low bacterial adherence and strong antibacterial properties in vitro against SA. Bactericidal inhibition lasted until day 11. Highest biocompatibility was achieved using gentamicin palmitate GP1.75% coated ePTFE grafts. ePTFE grafts with gentamicin-coating are effective in vitro against SA growth and adherence. Most promising results regarding antimicrobial properties and biocompatibility were shown with chemically bounded gentamicin palmitate GP1.75% coatings. Graphical abstract.

Treatment of an Infected TEVAR with Extra- and Endovascular Bacteriophage Application

Introduction

Graft infections are severe complications. Surgical resection of infected aortic stent grafts is associated with high mortality and morbidity. Therefore, alternatives or adjuncts to antibiotic treatment and extensive surgery are urgently needed.

Report

A 67 year old woman was admitted with a methicillin sensitive Staphylococcus aureus infected stent graft in the thoracic aorta. Local infection was confirmed by PET-CT imaging. Surgical resection of the stent graft was not feasible because of comorbidities. Therefore, a three step approach for local bacteriophage treatment was performed as a last resort treatment. Firstly, the para-aortic tissue was debrided via left thoracotomy, a bacteriophage suspension was applied on the outer surface of the aorta, and a vacuum irrigation system was installed. After repeated alternating instillation of the bacteriophage suspension for three days, as a second step, the vacuum sponges were removed and a bacteriophage containing gel was applied locally on the outer surface of the aorta. In the third step, the bacteriophage containing gel was applied to a thoracic stent graft, which in turn was placed endovascularly into the infected stent.

Discussion

After 28 days, the patient was discharged from hospital with normalised infection parameters. PET-CT imaging at three and 12 months post-intervention did not show signs of infection in or around the thoracic aorta. This Case demonstrates successful treatment of an infected endovascular stent graft by application of bacteriophages both to extravascular and, as a novel approach, endovascular sites using a bacteriophage coated stent graft.

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Vascular graft infections are severe complications in vascular surgery.

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Bacteriophages are viruses that have lytic activity against specific bacteria.

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An infected stent graft in the thoracic aorta was treated with bacteriophages.

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Bacteriophages were applied both endo- and extravascularly.

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Local bacteriophage application was combined with systemic antibiotic treatment.

Polycatecholamine and gentamicin as modifiers for antibacterial and blood-biocompatible polyester vascular prostheses

Polyester (PET) prostheses are commonly used in reconstructive vascular surgery. The most serious complication after implantation is early or late infection of the graft. Therefore, there is high demand to protect prosthesis against bacterial adhesion and biofilm development. For this reason, in this work PET prostheses were first coated by highly adhesive polycatecholamine layer. The grafts were then coupled with gentamicin and studied in relation to morphological and structural properties, biological safety (contact with blood, reaction of vascular endothelial cells (HUVEC), Danio rerio fish), drug release and antibacterial activity. Among two tested catecholamine monomers, L-DOPA was found to be more effective precursor in this process than dopamine. For L-DOPA, assistance of Cu²⁺, Mg²⁺ and Na⁺ ions seems to increase the amount of further immobilized drug. Coated prostheses exhibited greater human endothelial cell proliferation increase and lower cytotoxic effect than uncoated. The modification reduced the hemolysis observed for pristine commercial graft and limited the rate of abnormalities in D. rerio larvae, confirming the safety of the proposed modification. The coating allowed to double the amount of immobilized antibiotic in comparison with uncoated graft which resulted in increased antibacterial activity and reduced bacterial adhesion against 4 bacterial strains prevalent in biomaterials infections. Overall, poly(L-DOPA)-coatings deposited on PET vascular grafts can effectively functionalize these prostheses for higher safety in biomedical applications.

Pre-clinical In Vitro Models of Vascular Graft Coating in the Prevention of Vascular Graft Infection: A Systematic Review

OBJECTIVE

Vascular graft infection (VGI) is a feared complication. Prevention is of the utmost importance and vascular graft coatings (VGCs) could offer a potential to do this, with in vitro research a first crucial step. The aim of this study was to summarise key features of in vitro models investigating coating strategies to prevent VGI in order to provide guidance for the setup of future translational research.

DATA SOURCES

A comprehensive search was performed in MEDLINE, Embase, and Web of Science.

METHODS

A systematic review was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-analyses guidelines. For each database, a specific search strategy was developed. Quality was assessed with the Toxicological data Reliability Assessment Tool (ToxRTool). In vitro models using a VGC and inoculation of the graft with a pathogen were included. The type of graft, coating, and pathogen were summarised. The outcome assessment in each study was evaluated.

RESULTS

In total, 4 667 studies were identified, of which 45 papers met the inclusion criteria. The majority used polyester grafts (68.2%). Thirty-one studies (68.9%) included antibiotics, and nine studies (20%) used a commercial silver graft in their protocol. New antibacterial strategies (e.g., proteolytic enzymes) were investigated. A variety of testing methods was found and focused mainly on bacterial adherence, coating adherence and dilution, biofilm formation, and cytotoxicity. Ninety-three per cent of the studies (n = 41) were considered unreliable.

CONCLUSION

Polyester is the preferred type of graft to coat on. The majority of coating studies are based on antibiotics; however, new coating strategies (e.g., antibiofilm coating) are coming. Many in vitro setups are available. In vitro studies have great potential, they can limit the use, but cannot replace in vivo studies completely. This paper can be used as a guidance document for future in vitro research.

The Influence of 3D Printed Aortic Models on the Evolution of Physician Modified Stent Grafts for the Urgent Treatment of Thoraco-abdominal and Pararenal Aortic Pathologies

OBJECTIVE

The aim was to describe the outcomes of high risk patients with symptomatic or contained rupture of pararenal (PRAs) and thoraco-abdominal aortic aneurysms (TAAAs) with anatomy unsuitable for commercially available stent grafts who underwent fenestrated endovascular aneurysm repair (FEVAR) using physician modified stent grafts (PMSGs) planned with 3D image analysis software (3DIMAS), and 3D printed aortic models (3DAMs).

METHODS

Nineteen consecutive patients (17 male; mean age, 70 ± 9 years) underwent PMSG-FEVAR between 2015 and 2019. 3DAMs to plan the PMSGs were introduced in 2018. End points were all cause mortality, freedom from any endoleak, target vessel patency, and re-intervention.

RESULTS

Seven patients (36.8%) were treated with PMSGs using 3DIMAS (three PRAs, three type IV, and one type III TAAAs), and 12 patients (63.2%) received PMSGs using 3DAMs (five PRAs, seven type IV TAAAs). Six patients presented with contained aortic rupture and 13 patients were treated for symptomatic aortic aneurysm. Mean aortic diameter was 72 ± 10 mm. The choice of stent graft for fenestration was the Valiant Captivia Closed Web (Medtronic), except for one patient. Sixteen (84.2%) stent grafts were manufactured with four fenestrations. Technical success was 100%. Seventy-one renovisceral branch vessels were targeted with fenestrations. Mean length of hospital stay was 17.3 ± 10.4 days. Thirty day mortality was 0%. Two patients developed reversible spinal cord injury. Mean follow up was 14.4 months (range 1-52 months). During follow up one non-aneurysm related death occurred, and two successful re-interventions were performed: one to re-establish renal artery patency, and one to treat a type 1c endoleak.

CONCLUSION

PMSGs for urgent treatment of pararenal and thoraco-abdominal aortic aneurysms in high risk patients unsuitable for commercially available stent grafts are feasible and safe. 3D printing technology may improve urgent construction of patient specific devices for treatment of complex aortic pathologies and improve outcomes.

Efficacy of antiseptic impregnation of aortic endografts with rifampicin compared to silver against in vitro contamination with four bacteria that frequently cause vascular graft infections

OBJECTIVE

This in vitro study investigates the antimicrobial efficacy of impregnation of commercially available aortic endografts (EG) with rifampicin (RIF) and nanocolloidal silver.

METHODS

Endografts were flushed with 50 mL of RIF 600 mg, 70 mL of a silver-based aqueous solution (AG), or 50 mL of phosphate-buffered saline (PBS) over 15 minutes. Endografts were then retrieved from the sheath and cut in 1 × 1 cm sized graft units (n = 80 of each impregnation), which were then incubated for 1 hour separately with inoculates containing 10⁶ or 10³ bacteria per milliliter (bact/mL) of each of the following bacteria: Staphylococcus epidermidis, Escherichia coli, multisensitive Staphylococcus aureus, and Pseudomonas aeruginosa. After sonication of the graft units, bacterial counts were measured by plating out twice the sonication solution on Mueller-Hinton plates.

RESULTS

RIF showed a statistically significant decrease of colony forming units per milliliter for all four bacterial strains in both concentrations compared with PBS and AG, except for 10³ bact/mL of E coli. AG showed a significant decrease of colony forming units per milliliter compared with PBS only for 10⁶ bact/mL of E coli and was statistically significantly inferior to RIF for all four bacterial strains in both concentrations with the exception of E coli at a concentration of 10³ bact/mL.

CONCLUSIONS

This in vitro study demonstrated infectivity resistance of aortic EG after flushing with RIF. Moreover, the feasibility of flushing aortic EG with a new silver-based agent could be demonstrated, but without statistically significant antimicrobial efficacy compared with native EG.

Serine Protease Inhibitors-New Molecules for Modification of Polymeric Biomaterials

Three serine protease inhibitors (AEBSF, soy inhibitor, α₁-antitrypsin) were covalently immobilized on the surface of three polymer prostheses with the optimized method. The immobilization efficiency ranged from 11 to 51%, depending on the chosen inhibitor and biomaterial. The highest activity for all inhibitors was observed in the case of immobilization on the surface of the polyester Uni-Graft prosthesis, and the preparations obtained showed high stability in the environment with different pH and temperature values. Modification of the Uni-Graft prosthesis surface with the synthetic AEBSF inhibitor and human α₁-antitrypsin inhibited the adhesion and multiplication of Staphylococcus aureus subs. aureus ATCC^® 25923^TM and Candida albicans from the collection of the Department of Genetics and Microbiology, UMCS. Optical profilometry analysis indicated that, after the immobilization process on the surface of AEBSF-modified Uni-Graft prostheses, there were more structures with a high number of protrusions, while the introduction of modifications with a protein inhibitor led to the smoothing of their surface.

Conventional culture diagnostics vs. multiplex PCR for the detection of causative agents of vascular graft infections - results of a single centre observational pilot study

Background: Timely diagnosis of vascular graft infections is of major importance in vascular surgery. The detection of causative microorganisms is needed for specific medical treatment, but conventional culture is often slow, insensitive and inconclusive due to antibiotic pre-treatment. Detection of bacterial DNA by polymerase chain reaction (PCR) might bypass these problems. We hypothesised that multiplex PCR (mPCR) is feasible, fast and sensitive to detect causative microorganisms in vascular graft infections. Patients and methods: We performed a pilot observational prospective study comparing conventional culture and a commercial mPCR. Inclusion criteria were: confirmed graft infection, suspicious imaging, clinical suspicion, anastomotic aneurysm and repeated graft occlusion. Diagnostic methods were performed using identical samples. Time to result, microorganisms and antibiotic resistance in both groups were compared using Student's t-test or nonparametric tests. Results: 22 samples from 13 patients were assessed and 11 samples were negative for bacteria. Some showed multiple germs. In total, we found 15 different organisms. 13 samples matched, 9 had non-concordant results. Out of the mismatches 3 microorganisms identified in PCR were not detected by culture. Time to result with PCR was shorter (median 5 h vs. 72 h, p < 0.001) than with culture. No resistance genes were detected by mPCR, but conventional culture allowed susceptibility testing and revealed resistance in 5 samples. Conclusions: mPCR seems to be a feasible and quick tool to detect causes of vascular graft infections within 24 h and might be helpful in antibiotic pre-treated patients. The detection of antibiotic resistance with mPCR needs improvement for clinical practice.

Histoplasmosis Infection of Aortobifemoral Graft Treated with a Neoaortoiliac System

Aortic graft infections are a feared complication of aortic bypass operations and impart significant morbidity and mortality when they occur. The most common etiology is bacterial, with a presentation ranging from subclinical to acutely symptomatic depending on the organism. Fungal infections of prosthetic grafts are rare, especially in immunocompetent patients. Graft infections remain a clinical diagnosis. We report a rare case of an aortobifemoral graft infection with Histoplasma capsulatum that was diagnosed on surgical pathology, as the preoperative infectious evaluation was negative. The neoaortoiliac system operation was successfully used to solve this patient's highly morbid condition.

Daptomycin treatment in Gram-positive vascular graft infections

BACKGROUND

Daptomycin is a bactericidal antibiotic approved for the treatment of skin and soft tissue infections and right-side endocarditis. However, there is a lack of published data outlining its usefulness in vascular graft infections (VGI). The aim of this study was to describe the clinical experience of daptomycin use in the treatment of VGI caused by Gram-positive bacteria.

METHODS

This was a retrospective cohort study of patients diagnosed with VGI receiving daptomycin at a tertiary care hospital during the period January 2010 to December 2012.

RESULTS

Of a total 1066 consecutive patients who had undergone vascular grafts (VG), 25 were diagnosed with VGI. Fifteen of these patients (11 prosthetic VG, three autologous VG, one both types) received daptomycin (median dose 6.7mg/kg/day, range 4.1-7.1mg/kg/day; median age 69 years, range 45-83 years; 80% male). The infected bypass was removed in 13 cases. The most common reason for selecting daptomycin was kidney failure (53%). The Gram-positive organisms isolated were coagulase-negative Staphylococcus (n=10), Staphylococcus aureus (n=3) (two methicillin-resistant S. aureus), Enterococcus faecium (n=2), and Enterococcus faecalis (n=1). The mean follow-up was 69 months (interquartile range 48-72 months). Ten patients (66.7%) achieved complete healing of the VGI. A recurrence of the infection was observed in 100% of patients in whom the bypass was not removed. Among patients who did not achieve complete healing, one needed a supracondylar amputation and one died as a consequence of infection. Five patients received treatment with rifampicin in addition to daptomycin and they were all cured.

CONCLUSIONS

The use of daptomycin and surgery for Gram-positive VGI was effective and well tolerated, and this may be a good alternative for the treatment of VGI in patients with peripheral arterial disease in whom renal insufficiency is common.

Rapid in Vitro Quantification of S. aureus Biofilms on Vascular Graft Surfaces

Objectives: Increasing resistance of microorganisms and particularly tolerance of bacterial biofilms against antibiotics require the need for alternative antimicrobial substances. S. aureus is the most frequent pathogen causing vascular graft infections. In order to evaluate the antimicrobial efficacy, quantification of the bacterial biofilms is necessary. Aim of the present study was the validation of an in vitro model for quantification of bacterial biofilm on vascular graft surfaces using three different assays. Methods: Standardized discs of vascular graft material (Dacron or PTFE) or polystyrene (PS) as control surface with 0.25 cm² surface area were inoculated with 10^-3 diluted overnight culture of three biofilm-producing S. aureus isolates (BEB-029, BEB-295, SH1000) in 96-well PS culture plates. After incubation for 4 and 18 h, the biofilm was determined by three different methods: (a) mitochondrial ATP concentration as measure of bacterial viability (ATP), (b) crystal violet staining (Cry), and (c) vital cell count by calculation of colony-forming units (CFU). The experiments were performed three times. Quadruplicates were used for each isolate, time point, and method. In parallel, bacterial biofilms were documented via scanning electron microscopy. Results: All three methods could quantify biofilms on the PS control. Time needed was 0:40, 13:10, and 14:30 h for ATP, Cry, and CFU, respectively. The Cry assay could not be used for vascular graft surfaces due to high unspecific background staining. However, ATP assay and CFU count showed comparable results on vascular graft material and control. The correlations between ATP and CFU assay differed according to the surface and incubation time and were significant only after 4 h on Dacron (BEB-029, p = 0.013) and on PS (BEB-029, p < 0.001). Between ATP and Cry assay on PS, a significant correlation could be detected after 4 h (BEB-295, p = 0.027) and after 18 h (all three strains, p < 0.026). The reproducibility of the ATP-assay presented as inter-assay-variance of 2.1 and as intra-assay variance of 8.1 on polystyrene. Conclusion: The in-vitro model reproducibly quantifies biofilm on standardized vascular graft surfaces with ATP assay as detection system. The ATP assay allows accelerated microbial quantification, however the correlation with the CFU assay may be strain- and surface-dependent.

Vascular Graft Impregnation with Antibiotics: The Influence of High Concentrations of Rifampin, Vancomycin, Daptomycin, and Bacteriophage Endolysin HY-133 on Viability of Vascular Cells

Background

Rifampin-soaked synthetic prosthetic grafts have been widely used for prevention or treatment of vascular graft infections (VGIs).

This in vitro study investigated the effect of the antibiotics daptomycin and vancomycin and the new recombinant bacteriophage endolysin HY-133 on vascular cells, as potential alternatives compared to rifampin.

Material/Methods

Primary human ECs, vascular smooth muscle cells (vSMC), and fibroblasts were cultivated in 96-well plates and incubated with rifampin, daptomycin, vancomycin, and endolysin HY-133 for 24 h. Subsequently, after washing, cell viability was determined by measuring mitochondrial ATP concentration. Antibiotics were used in their corresponding minimum and maximum serum concentrations, in decimal multiples and in maximum soaking concentration. The experiments were performed in triplicate.

Results

The 10-fold max serum concentrations of rifampin, daptomycin, and vancomycin did not influence viability of EC and vSMC (100 μg/ml, p>0.170). Higher concentrations of rifampin (>1 mg/ml) significantly (p<0.001) reduced cell viability of all cell types. For the other antibiotics, high concentrations (close to maximum soaking concentration) were most cytotoxic for EC and vSMC and fibroblasts (p<0.001). Endolysin did not display any cytotoxicity towards vascular cells.

Conclusions

Results of this in vitro study show the high cytotoxicity of rifampin against vascular cells, and may re-initiate the discussion about the benefit of prophylactic pre-soaking in high concentrations of rifampin. Further studies are necessary to determine the influence of rifampin on the restoration of vessel functionality versus its prophylactic effect against VGIs. Future use of recombinant phage endolysins for alternative prophylactic strategies needs further investigations.

A Novel Mouse Model of Staphylococcus aureus Vascular Graft Infection: Noninvasive Imaging of Biofilm Development in Vivo

Staphylococcus aureus causes very serious infections of vascular grafts. Knowledge of the molecular mechanisms of this disease is largely lacking because of the absence of representable models. Therefore, the aim of this study was to set up a mouse model of vascular graft infections that closely mimics the human situation. A catheter was inserted into the right carotid artery of mice, which acted as a vascular graft. Mice were infected i.v. using 8 different S. aureus strains, and development of the infection was followed up. Although all strains had varying abilities to form biofilm in vitro and different levels of virulence in mice, they all caused biofilm formation on the grafts. This graft infection was monitored using magnetic resonance imaging (MRI) and ¹⁸F-fluordeoxyglucose positron emission tomography (FDG-PET). MRI allowed the quantification of blood flow through the arteries, which was decreased in the catheter after infection. FDG-PET revealed high inflammation levels at the site of the catheter after infection. This model closely resembles the situation in patients, which is characterized by a tight interplay between pathogen and host, and can therefore be used for the testing of novel treatment, diagnosis, and prevention strategies. In addition, combining MRI and PET with microscopic techniques provides an appropriate way to characterize the course of these infections and to precisely analyze biofilm development.