Bacterial adherence to vascular prostheses: A determinant of graft infectivity

An in vitro model was developed to quantitatively measure bacterial adherence to the surface of prosthetic vascular graft material. Four strains of bacteria (Staphylococcus aureus, nonmucin-producing S. epidermidis [SP-2], mucin-producing S. epidermidis [RP-12], and Escherichia coli) were used to inoculate expanded polytetrafluoroethylene (ePTFE), woven Dacron, and velour knitted Dacron graft material. After graft specimens were incubated in a 10⁷ suspension of bacteria, they were washed to remove nonadherent organisms and ultrasonically oscillated to dislodge adherent organisms. Quantitative culture of the sonication effluent was used to calculate bacterial adherence, expressed as the number of colony-forming units found in each square centimeter of graft material per 10⁷ inoculum. All bacterial strains had a greater affinity to velour knitted Dacron graft than to ePTFE (p < 0.025). E. coli and S. aureus adhered to velour knitted Dacron in greater numbers than to woven Dacron (p < 0.04). The production of extracellular polysaccharide (mucin) by the RP-12 strain significantly increased adherence to both ePTFE and Dacron grafts compared with the other three bacterial strains tested (p < 0.04). Although E. coli was less adherent to ePTFE than nonmucin-producing staphylococcal strains (S. aureus and SP-2), no difference in adherence to knitted or woven Dacron graft material was demonstrated. The differential adherence of bacteria to prosthetic vascular grafts pays an important role in the pathogenesis of graft sepsis and determines relative graft infectivity. The in vitro model developed is well suited for further study of the mechanisms by which bacteria adhere to and colonize vascular grafts. (J VASC SURG 1986;3:732-40.)     

Infection of vascular prostheses caused by bacterial biofilms

A canine model was developed to study the efficacy of graft replacement as treatment for vascular prosthesis infections from Staphylococcus epidermidis. Infrarenal aortic graft infections were established in 18 dogs by implantation of Dacron prostheses colonized in vitro with a slime-producing strain of S. epidermidis to form an adherent bacteria-laden biofilm (5 X 10(6) colony-forming units/cm2 graft). Study animals developed a graft infection with anatomic and microbiologic characteristics typical of late prosthetic graft infections in humans (sterile perigraft exudate, absent graft incorporation, and normal serum leukocyte count and sedimentation rate). The S. epidermidis study strain was isolated from 14 of 18 explanted grafts (78%) by mechanical disruption of the graft surface biofilm and culture in broth media. Four dogs with sterile graft cultures had histologic evidence of bacterial infection. The established prosthetic surface biofilm infection was treated by graft excision, parenteral cefazolin, and graft replacement with a Dacron or polytetrafluoroethylene (PTFE) vascular prosthesis. One month after graft replacement, no PTFE graft had signs of infection, but perigraft exudate and inflammation involved three of nine Dacron grafts (33%). The study strain was recovered from four of nine PTFE grafts (44%) and two of nine Dacron (22%) replacement grafts (p greater than 0.05). Prosthetic replacement of Dacron prostheses infected by S. epidermidis as a bacteria-laden surface biofilm can result in early graft healing, but persistent colonization of one third of replacement grafts signify that recurrent clinical infection remains a risk.     

In situ replacement of vascular prostheses infected by bacterial biofilms

Late prosthetic graft infections are commonly the result of coagulase-negative staphylococci that survive within a biofilm on prosthetic surfaces and provoke perigraft inflammation. The indolent nature and microbiologic characteristics of bacterial biofilm infections coupled with the morbidity of graft excision and extraanatomic bypass grafting prompted us to use in situ graft replacement in 15 patients admitted to the hospital with 17 infected graft segments at a mean (+/- SEM) time interval of 70 +/- 16 months after graft implantation (n = 6) or revision (n = 9). Since 1986, 17 grafts (14 aortofemoral, 2 axillofemoral, and 1 femoropopliteal) infected by bacterial biofilms have been treated. Signs on admission included femoral pseudoaneurysm (n = 7), perigraft abscess (n = 6), or graft-cutaneous sinus tract (n = 4). No patient exhibited septicemia. At operation graft incorporation was absent and Gram's stain of perigraft exudate showed polymorphonuclear leukocytes but no bacteria. Culture of explanted graft material isolated coagulase-negative staphylococci (n = 12), Staphylococcus aureus (n = 1), and no growth (n = 2). All patients were successfully treated by a regimen that included parenteral antibiotics, removal of involved graft material, excision of inflamed perigraft tissue, and in situ replacement with an expanded polytetrafluoroethylene prosthesis. No deaths, graft thromboses, or deep wound infections occurred after operation. Recurrent graft infection did not develop during a follow-up interval that ranged from 5 to 50 months (mean, 21 months). Diagnosis of vascular prosthesis infection caused by bacterial biofilms can be based on signs at admission and operative findings. Complications of this perigraft infection can be eradicated by antibiotic administration, local debridement, and in situ graft replacement.     

Inhibition of bacterial adhesion by antibacterial surface pretreatment of vascular prostheses

Polytetrafluoroethylene grafts were pretreated with oxacillin, with the cationic detergent benzalkonium, or with both substances, either at room temperature or at 90 degrees C. Inhibition zones ranging from 6.4 to 15.2 mm formed around all grafts incubated on Staphylococcus aureus-streaked agar plates except control disks and those treated with oxacillin. Treated grafts were exposed in vitro to S. aureus in high concentration, followed by distilled water lavage. The graft surface was then stained with ruthenium red to stain polysaccharides and studied by scanning and transmission electron microscopy. Colonization of the graft surface by adhesive bacteria was demonstrated in all cases, although it was less prevalent on grafts pretreated with benzalkonium bound at 90 degrees C.     

The effect of pentosanpolysulphate and carbenoxolone on bacterial adherence to the injured urothelium

The effect of the glycosaminoglycan (GAG) layer on the adherence of Escherichia coli to the bladder urothelium of rats has been studied. The study was performed by destroying the GAG layer and the changes were observed using the electron microscope. Bacterial adherence to the bladder with a destroyed GAG layer was much higher than to the normal bladder. Following the destruction of the GAG layer, the instillation of sodium pentosanpolysulphate significantly reduced the adhesion of bacteria. Prophylactic intramuscular administration of carbenoxolone increased the speed of regeneration of the destroyed GAG layer.     

The effect of aspirin on adherence of slime-producing, coagulase-negative staphylococci to vascular grafts

In this study, we examined the adherence of slime-producing standard Staphylococcus epidermidis strain ATCC 12228 to Dacron and polytetrafluoroethylene (PTFE) grafts in in vitro medium either containing salicylate or not. Dacron and PTFE graft pieces of standard size were placed in trypticase soy broth either containing 5 mM acetylsalicylic acid solution or not. These soy broths also contained 1 x 10(7) colony-forming units/mL S. epidermidis ATCC 12228. The incubation period lasted for 18 hr at 37 degrees C. The bacteria on the graft were freed by vortexing. The obtained bacteria suspension was diluted serially. Afterward, the suspension was plated on 5% sheep blood agar and counted after overnight incubation. In this study, we demonstrate that aspirin of an ideal concentration (5 mM) decreased the adherence of slime-producing S. epidermidis strain to Dacron and PTFE grafts. The mean number of colonies was significantly lower for both Dacron and PTFE groups in salicylated medium. We believe that aspirin provided in the postoperative period can, by maintaining the ideal serum level, decrease graft infections emerging due to coagulase-negative staphylococcus.     

The postantibiotic effect of azithromycin on respiratory pathogens

We assessed the post-antibiotic effect (PAE) of azithromycin against 3 strains of Streptococcus pneumoniae 2 strains of Haemophilus influenzae and 2 strains of Moraxella catarrhalis. The strains were exposed for 2 hours to a concentration of 0.5 mg/l. A stationary phase inoculum of 1 x 10(6)-5 x 10(6) CFU/ml in IsoSensitest Broth with 5% lysed horse blood and 20 mg/l NAD was used and shaken for the duration of the experiment. Antibiotic was neutralised by dilution 1:1000 into pre-warmed medium. [table: see text] In conclusion, even at such low concentration as achieved in serum, azithromycin has a PAE against the respiratory pathogens studied. In our opinion this could allow the use of azithromycin, in the usual regimen even in bacteremic respiratory infections.     

Infection of vascular prostheses

Graft infection occurred in 11 of 322 patients (3.4%) who had insertion of a vascular prosthesis for peripheral vascular disease during a 4-year period. The groin was the most common site of infection and multiple resistant Staphylococcus aureus (MRSA) was the most common organism responsible. Six of 7 MRSA infections occurred following a procedure involving a previously placed graft and/or a groin incision. Prophylactic antibiotics effective against MRSA are recommended for patients having a revisional procedure, especially involving the groin.     

Studies on the elastic properties of vascular prostheses

The difference of mechanical properties between a vascular prosthesis and its host arteries is suggested to be a contributing factor in graft failure and different methods have been used to evaluate the elasticity of arterial graft. In this study, a new type ultrasonic displacement meter combined with B-mode imaging was developed and dynamic compliance of four types of arterial grafts currently available for clinical use, human saphenous vein, human umbilical vein, velour Dacron and expanded polytetrafluoroethylene (EPTFE), were measured in vitro and in vivo. Dynamic compliance was derived from intraluminal pulsatile pressure and diameter change of the vessel obtained from the displacement meter. The in vitro examination showed that the human umbilical vein was the most compliant among human saphenous vein, velour Dacron and EPTFE. The human saphenous vein was compliant in low intraluminal pressure less than 50 mmHg, and became more stiff than the human umbilical vein with increasing pressure. After experimental implantation, the compliance of human umbilical vein and EPTFE showed similar characteristics in vitro, with the exception of velour Dacron, which was progressively less compliant. In comparison of compliance of human arteries to that of arterial grafts, a mismatch in compliance between grafts and host arteries was obviously demonstrated.     

The effect of dexamethasone and endotoxin administration on biliary IgA and bacterial adherence.

Adherence of bacteria to the intestinal epithelial cell may be the crucial initiating event for invasion and translocation and is normally prevented by both immune (IgA) and nonimmune (mucus, peristalsis, desquamation) mucosal defense mechanisms. The purpose of the present study was to examine the effect of endotoxin administration on mucosal immunity and to define the role of glucocorticoids, commonly released during endotoxicosis, in this process. Thirty female Fisher rats were randomly assigned to three groups of 10 animals each. Group I (CONT), was fed rat chow and H2O ad lib., Group II (DEX) was administered 0.8 mg/kg subcutaneously of dexamethasone, and Group III (ETX) was given 1 mg/kg of endotoxin. Twenty-four hours later animals were sacrificed and mesenteric lymph nodes and vigorously washed stool-free ceca were collected and cultured. Bile was collected and assayed for IgA from 5 animals in each group. A significant decrease (P < 0.05) in secretory IgA was noted in animals treated with either dexamethasone or endotoxin (CONT = 332 +/- 42, DEX = 78 +/- 24, ETX = 68 +/- 16 micrograms/mg protein +/- SEM). No difference in S-IgA between animals in the dexamethasone-treated group and the endotoxin-treated group was noted (P = NS). A statistically significant increase (P < 0.001) in bacteria adherent to the cecal wall in both the dexamethasone-treated rats and the endotoxin-treated rats over that in = 7.5 +/- 0.8, CONT = 6.4 +/- 0.6 cfu/g(log10) +/- SD). Our results suggest that endotoxin or glucocorticoid administration results in significant bacterial adherence to the cecal mucosa and a decrease in IgA.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effect of bacterial contamination on neointimal hyperplasia in vascular grafts

Neointimal hyperplasia (NH) is the most significant contributing factor to long-term vascular graft failure. Inflammation is known to be important in its development; however, the role of bacterial infection is unclear. We examined the effect of contamination with common organisms on the development of NH in expanded polytetrafluoroethylene grafts. Thirty adult pigs were randomized into one of four groups: no infection, contamination with Staphylococcus aureus, mucin-producing Staphylococcus epidermidis, or Pseudomonas aeruginosa. An expanded polytetrafluoroethylene graft (6 mm x 3 cm) was placed as a common iliac artery interposition graft and was inoculated with 1-2 x 10(8) of the selected organism before closure. Grafts were explanted 6 weeks postoperatively. Microbiologic, histological, and morphometric evaluations were performed. All grafts were patent at the time of euthanasia. The mean areas of NH were 5.45 mm(2) in sterile grafts, 8.36 mm(2) in S. aureus, 7.63 mm(2) in S. epidermidis, and 11.52 mm(2) in P. aeruginosa grafts. Comparison of means via analysis of variance showed that P. aeruginosa grafts had significantly higher formation of NH than sterile grafts (P = 0.025). NH production in infected grafts appears to be organism specific and is significantly higher with P. aeruginosa than common Gram-positive organisms. Increased NH from subclinical infection may be a significant factor contributing to late graft failures.     

Reduction of bacterial adherence to catheter surface with heparin

Despite many advances in catheter design and use, the most common cause of hospital-acquired infections is catheterization of the urinary tract. In the present investigation the adherence of bacteria to catheters coated with heparin was studied. Since heparin itself does not coat the plastic catheter surface, a complex of heparin with tridodecylmethylammonium chloride (TDMAC) was used which results in hydrophobic association of hydrocarbon chains of the TDMAC with the catheter leaving the quaternary ammonium moiety of TDMAC exposed to the surface forming ionic bonds with the highly anionic sulfate groups of heparin. Coating latex catheter material with TDMAC without heparin resulted in 3.6-fold higher adherence whereas coating with the TDMAC-heparin complex reduced adherence to less than 10% of control untreated latex. TDMAC-heparin also significantly reduced bacterial adherence to teflon coated latex (Bardex) and vinyl catheter material. Less than 30% of the original heparin was removed after wash periods of up to one week. These results indicate that TDMAC-heparin coating of urethral catheters reduces bacterial adherence and thereby may delay the acquisition of catheter associated urinary tract infection.     

Recognition and treatment of vascular steal secondary to hemodialysis prostheses

Ischemic symptoms of the distal extremity developed in 4 patients from a group of 55 in whom a primary polytetrafluorethylene prosthesis was placed for purpose of hemodialysis. Diagnosis of vascular steal syndrome was suggested by clinical symptoms of pain and coolness of the distal part, as well as trophic changes of the hand. The diagnosis was confirmed by placing a cuffed photoplethysmograph transducer on one or more of the digits of the affected limb and recording the waveform before and during manual compression of the arterial end of the prosthesis. The findings showed essentially a flat waveform converting to pulsatile waveform when the proximal graft was compressed. Two patients underwent controlled operative banding of the arterial end of the polytetrafluoroethylene prosthesis using this same method. A polytetrafluoroethylene cardiovascular patch was cut to a width of 1 cm and then cut again to form two shoelace tails each 0.5 cm in width. The band was placed around the proximal part of the prosthesis and progressively tightened until an adequate digital pulse wave returned. Preservation of flow through the prosthesis was maintained so as to allow dialysis and prevent thrombosis. The technical aspects of the procedure have been discussed. Vascular steal syndrome appears to be more common in the diabetic.