Evaluation of Gram-Positive and Gram-Negative Bacterial Adherence on Four Different Vascular Prosthetic Grafts In Vitro

Research Article

Austin J Surg. 2019; 6(15): 1200.

Evaluation of Gram-Positive and Gram-Negative Bacterial Adherence on Four Different Vascular Prosthetic Grafts In Vitro

Ruemke S1,2*, Rubalskii E1,2, Mashaqi B1, Burgwitz K1,2, Haverich A1,2, Salmoukas C1,2 and Kuehn C1,2

¹Department of Cardiac, Thoracic, Transplantation and Vascular Surgery, Hannover Medical School, Germany

²Lower Saxony Centre for Biomedical Engineering, Implant Research and Development, Germany

*Corresponding author: Ruemke S, Department of Cardiac, Thoracic, Transplantation and Vascular Surgery, Hannover Medical School, Carl-Neuberg-Str. 1, D-30625 Hannover, Germany

Received: June 13, 2019; Accepted: July 19, 2019; Published: July 26, 2019


Objectives: The aim of this study was to evaluate the adherence capability of clinically used vascular grafts (Uni-Graft® KD V, Silver Graft, Gelweave™ and Gore® Propaten®) against Staphylococcus epidermidis, Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa and to assess efficacy of the graft impregnation with vancomycin/gentamicin solution.

Methods: Each graft type was cut into 1cm2 samples and was separately contaminated with suspensions of bacteria mentioned above. Experimental group of grafts was tested after antibiotic impregnation; the controls remained without any impregnation. After 24h incubation OD600nm measurement of the supernatant solution and CFU count of the adhered bacteria were performed.

Results: Antibiotic impregnation led to a significantly reduced OD600nm after incubation for all grafts and bacteria. Untreated grafts contained on their surface more than 105 CFU/cm2. Antibiotic treatment completely prevented all grafts from S. epidermidis adhesion.

S. aureus: After antibiotic impregnation Uni-Graft® KD V, Gelweave™ and Silver Graft were sterile. Gore® Propaten® showed no significant reduction of adhesion.

E. coli: After previous impregnation of Silver Graft and Uni-Graft® KD V remained sterile, whereas the Gelweave™ and Gore® Propaten® showed a nonsignificant reduction of bacterial count.

P. aeruginosa: Antibiotic impregnation led to significant reduction of adhered bacteria for Uni-Graft® KD V and Silver Graft. Gelweave™ and Gore® Propaten® showed no significant differences in CFU count.

Conclusion: This study showed that the antibiotic impregnation of vascular grafts with vancomycin/gentamicin solution is a feasible and easy to implement prophylactic measure to prevent Gram-positive and Gram-negative bacterial growth and adhesion to cardiovascular prosthetic materials.

Keywords: Vascular graft; Antibiotic impregnation; Bacterial adherence


CFU: Colony Forming Units; OD: Optical Density; SD: Standard Deviation; CI: Confidence Interval; PET: Polyethylene Terephtalat; ePTFE: Expanded Polytetrafluorethylene; TSB: Tryptic Soy Broth; TSA: Tryptic Soy Agar


Bacterial colonization and infection of implanted devices, especially vascular prosthetic grafts, is a feared complication due to the life-threatening consequences, significantly increasing patient mortality and morbidity. The incidence of prosthetic vascular graft infection ranges from 1-6%, depending on the location and type of the graft [1-3].

Infections can be divided into early and late vascular graft infections. In early vascular graft infection, S. aureus and coagulasenegative staphylococci (e.g. S. epidermidis) account for approximately 60-70% of VGI cases, while Gram-negative species like Pseudomonas aeruginosa and Escherichia coli are also common [4]. An early infection on a medical implant is initiated by bacterial adhesion on the graft surface. A major hindrance to treatment of graft infections is bacterial biofilm formation on the graft surface. Biofilms are a community of bacteria that adhere to each other and are embedded in a self-produced extracellular matrix that is highly resistant to host immune defenses and the penetration of antibiotics [5,6].

For this in vitro study, we tested four of the most common Gram-positive and Gram-negative bacteria involved in vascular graft infection on four different, clinically used vascular prosthetic grafts, in order to investigate possible differences in the amount of bacterial adherence on the different graft surfaces and to provide recommendations for the individual clinical use.

Furthermore we investigated, if an antibiotic impregnation of the grafts is a suitable method in preventing bacterial adherence to the graft materials.

Materials and Methods

Antibiotic agents

An antibiotic solution consisting of vancomycin and gentamicin was prepared. For this purpose, 1 g of vancomycin (Hikma Farmaceutica S.A., Terrugem, Portugal) was dissolved in 125 ml of 0.9% NaCl (B. Braun, Melsungen, Germany) and thus a solution with the concentration of 8 mg/ml vancomycin was prepared. Three ampoules of gentamicin (Ratiopharm, Ulm, Germany) (240 mg/6 ml) were mixed with 94 ml of 0.9% NaCl and thus reached a concentration of 2.4 mg/ml. Subsequently, both solutions were mixed in the ratio 1:1 and reached a final concentration of 4 mg/ml vancomycin and 1.2 mg/ml gentamicin. The solution was made under sterile conditions and according to the manufacturer’s instructions.

Bacterial strains

The bacterial strains used in this study were 20231DSMZ for Staphylococcus aureus, 20044DSMZ for Staphylococcus epidermidis, 1103DSMZ for Escherichia coli and 19880DSMZ for Pseudomonas aeruginosa. The bacteria were sub-cultured on tryptic soy agar (Oxoid, Hampshire, UK) according to the recommendations of the German Collection of Microorganisms and Cell Cultures GmbH (www.dsmz.de). Dilution of the overnight cultures was performed with tryptic soy broth (TSB). The optical density (OD600nm) used for graft contamination was 0.2. This OD corresponds to approximately 1 × 108 colony-forming units (CFUs) per millilitre for S. aureus, 1 × 106 CFUs per mL for S. epidermidis, 1 × 107 CFUs per mL for E. coli and 1 × 107 CFU per mL for P. aeruginosa.

Vascular grafts

The following four vascular graft prostheses were used (Table 1): Knitted double-velour vascular grafts made of fine polyester fibres [polyethylene terephthalate (PET; Dacron)] and impregnated with absorbable bovine gelatine (Uni-Graft®, B. Braun/Aesculap, Tuttlingen, Germany); double-velour vascular grafts made of fine polyester fibres (PET), impregnated with absorbable bovine gelatine (polygeline), coated with 0.07 – 0.16 mg/cm² silver on the outer graft surface (Silver Graft, B. Braun/Aesculap, Tuttlingen, Germany); gelatine sealed, woven polyester grafts (Gelweave™, Vascutek Terumo, Inchinnan, Renfrewshire, Scotland UK) and Gore® Propaten® grafts, made of expanded polytetrafluoroethylene (ePTFE) coated with heparin on the luminar surface (W. L. Gore & Associates, Inc., Flagstaff, Arizona, USA). All grafts were processed to 1 × 1 cm pieces under aseptic conditions.