In vitro adherence of bacteria to prosthetic vascular grafts

Study protocol of a prospective single-arm multicenter clinical study to assess the safety and performance of the aXess hemodialysis graft: The pivotal study

BACKGROUND

Arteriovenous grafts (AVGs) are used for patients deemed unsuitable for the creation of an autogenous arteriovenous fistula (AVF) or unable to await maturation of the AVF before starting hemodialysis. However, AVGs are prone to infection and thrombosis resulting in low long-term patency rates. The novel aXess Hemodialysis Graft consists of porous polymeric biomaterial allowing the infiltration by cells and the growth of neotissue, while the graft itself is gradually absorbed, ultimately resulting in a fully functional natural blood vessel. The Pivotal Study will examine the long-term effectiveness and safety of the aXess Hemodialysis Graft.

METHODS

The Pivotal Study is a prospective, single-arm, multicenter study that will be conducted in 110 subjects with end-stage renal disease who are not deemed suitable for the creation of an autogenous vascular access. The primary efficacy endpoint will be the primary patency rate at 6 months. The primary safety endpoint will be the freedom from device-related serious adverse events at 6 months. The secondary endpoints will include the procedural success rate, time to first cannulation, patency rates, the rate of access-related interventions to maintain patency, the freedom from device-related serious adverse events and the rate of access site infections. Patients will be followed for 60 months. An exploratory Health Economic and Outcomes Research sub-study will determine potential additional benefits of the aXess graft to patients, health care institutions, and reimbursement programs.

DISCUSSION

The Pivotal study will examine the long-term performance and safety of the aXess Hemodialysis Graft and compare the outcome measures with historical data obtained with other graft types and autogenous AVFs. Potential advantages may include superior long-term patency rates and lower infection rates versus currently available AVGs and a shorter time to first cannulation compared to an autologous AVF. As such, the aXess Hemodialysis Graft may fulfill an unmet clinical need in the field of hemodialysis access.

First-in-human feasibility study of the aXess graft (aXess-FIH): 6-Month results

OBJECTIVE

The creation of an arteriovenous fistula (AVF) is considered the most effective hemodialysis (HD) vascular access. For patients who are not suitable for AVF, arteriovenous grafts (AVGs) are the best access option for chronic HD. However, conventional AVGs are prone to intimal hyperplasia, stenosis, thrombosis, and infection. Xeltis has developed an AVG as a potential alternative to currently available AVGs based on the concept of endogenous tissue restoration. The results of the first 6-month follow-up are presented here.

METHODS

The aXess first-in-human (FIH) study [NCT04898153] is a prospective, single-arm, multicenter feasibility study that evaluates the early safety and performance of the aXess Hemodialysis Graft. A total of 20 patients with end-stage renal disease were enrolled across six European investigational sites.

RESULTS

At 6-months follow-up, all grafts were patent with primary and secondary patency rates were 80% and 100%, respectively. Three patients required a re-intervention to maintain graft patency, while one re-intervention was required to restore patency. One graft thrombosis and zero infections were reported.

CONCLUSION

The expected advantages of the novel aXess Hemodialysis Graft over conventional AVGs would be evaluated by the analysis on long-term safety and effectiveness during the 5-year follow-up of the currently ongoing trial.

Efficacy of Antiseptic Solutions in Treatment of Staphylococcus Aureus Infected Surgical Wounds with Patches of Vascular Graft: An Experimental Study in Rats

Background and objectives: Treatment of a prosthetic vascular graft infection (PVGI) remains a challenging problem in vascular surgery. The aim of this study was to design a novel rat model for treatment of peripheral vascular prosthesis infection caused by Staphylococcus aureus (S. aureus) and to determine the efficacy of different antiseptic solutions in suppressing or eradicating infection from the wound and the graft material itself. Materials and methods: A piece of Dacron vascular prosthesis was surgically implanted at the dorsum of 48 Wistar rats and the wounds were infected with 5 McFarland standard inoculum of S. aureus. Suppurating wounds were daily irrigated with different antiseptic solutions: octenidine dihydrochloride, povidone-iodine, chlorhexidine digluconate, and sterile saline. The antimicrobial action of antiseptics was defined according to their capability to eradicate bacteria from the graft surroundings and bacteriological examination of the graft itself. Extended studies on wound microbiology, cytology, and histopathology were performed with an additional group of 10 rats, treated with the most effective antiseptic-octenidine dihydrochloride. Results: Four-day treatment course with octenidine, povidone-iodine, and chlorhexidine resulted in 99.98% (p = 0.0005), 90.73% (p = 0.002), and 65.97% (p = 0.004) decrease in S. aureus colonies in wound washouts, respectively. The number of S. aureus colonies increased insignificantly by 19.72% (p = 0.765) in control group. Seven-day treatment course with octenidine eradicated viable bacteria from nine out of 10 wound washouts and sterilized one vascular graft. Conclusions: A reproducible rat model of PVGI with a thriving S. aureus infection was designed. It is a first PVGI animal model where different antiseptic solutions were applied as daily irrigations to treat peripheral PVGI. Seven-day treatment with octenidine eradicated bacteria from the wound washouts for 90% of rats and one vascular graft. Further studies are needed to investigate if irrigations with octenidine could properly cure vascular bed from infection to assure a successful implantation of a new synthetic vascular substitute.

Initial Inoculation Concentration Does Not Affect Final Bacterial Colonization of In vitro Vascular Conduits

BACKGROUND

Despite improved peri-operative care, prosthetic graft infections continue to cause substantial morbidity and mortality. Contemporary graft infection models have tested a conduit's infectability using varying concentrations without standardization. Using a static assay in vitro model, we sought to evaluate the impact of inoculation concentration on vascular conduit attachment.

METHODS

The 2-hour and 24-hour attachment of Staphylococcus aureus TCH1516 and Pseudomonas aeruginosa PA01-UW were determined on polytetrafluoroethylene (PTFE), Dacron^®, nitinol, cobalt chromium, and Viabahn^® (W.L. Gore and Associates, Newark, DE) endoprotheses. Individually and in combination, concentrations at 10⁴, 10⁵, 10⁶, 10⁷, and 10⁸ were tested on 2-mm sections of each graft. After each time interval, the prosthetics were rinsed to remove non-attached bacteria, sonicated to release the attached bacteria, spiral plated, and then analyzed for the attached concentration.

RESULTS

After two hours, the higher initial inoculation concentration translated into a higher attachment percentage, but the mean attachment percentage was only 14.8% in the 10⁸ group. Pseudomonas aeruginosa had the greatest mean attachment across all material and concentration groups. The sequence of attachment on the conduits followed a constant order: Dacron, PTFE, cobalt, nitinol, and Viabahn with no difference between Dacron and PTFE. Although there were still differences at the 24-hour mark, the median attachment at each concentration was greater than the highest initial concentration (10⁸).

CONCLUSIONS

Initial attachment percentage is poor consistently regardless of inoculation concentration, however, Staphylococcus aureus and Pseudomonas aeruginosa are still able to achieve full attachment after 24 hours. A concentration of less than 10⁷ should be used in vascular graft infection models to ensure adequate bacterial attachment.

Development of an infection-resistant bifunctionalized Dacron biomaterial

A novel infection-resistant biomaterial was created by applying the antibiotic Ciprofloxacin (Cipro) to a recently developed bifunctionalized polyethylene terephthalate ("polyester," Dacron) material using textile-dyeing technology. Dacron was modified via exposure to ethylenediamine (EDA) to create amine and carboxylic acid sites within the polymer backbone. Cipro was applied to the bifunctionalized Dacron construct under varied experimental conditions, with resulting antimicrobial activity determined via zone of inhibition. Dacron segments treated at a liquor ratio of 20:1, with 5% Cipro on weight of fabric (owf), at pH 8 for 4 h at 70 degrees C followed by autoclaving showed antimicrobial activity for 78 days (length of study). Segments treated similarly but without autoclaving lost activity within 1 day. Dyeing time and temperature did not significantly affect antibiotic release/activity, but segments dyed at pHs higher or lower than 8 had less antimicrobial activity. The long-term infection resistance provided by this technique may answer major problems of infection from which implantable Dacron biomedical devices suffer.

Evaluation of polytetrafluoroethylene suture for frontalis suspension as compared to polybutylate-coated braided polyester

PURPOSE

To evaluate the efficacy of polytetrafluoroethylene (Gore-Tex) suture as compared to polybutylate-coated braided polyester (Ethibond) suture as sling materials for frontalis suspension in bilateral congenital ptosis.

METHODS

Frontalis sling surgery by modified Crawford's double triangle technique was performed on 30 patients (60 eyes) with bilateral ptosis. The patients were randomized into two groups depending on the type of suture material used: polytetrafluoroethylene or braided polyester.

RESULTS

Polytetrafluoroethylene suture achieved a statistically significant better and more stable ptosis correction, with slightly more lagophthalmos, than braided polyester suture over a mean (+/- SD) follow-up period of 16 +/- 3.24 months. There were more postoperative complications with braided polyester suture, but the difference was not statistically significant.

CONCLUSION

This is the first clinical study in which polytetrafluoroethylene in the form of suture has been studied. Polytetrafluoroethylene suture was found to be a safe and effective sling material for frontalis suspension and it can be recommended for clinical use.

Attachment of Staphylococcus aureus to eukaryotic cells and experimental pitfalls in staphylococcal adherence assays: a critical appraisal

Staphylococcus aureus is a bacterial species with pathogenic potential to both humans and animals. The primary natural niche is said to be the human vestibulum nasi from where bacterial cells may spread to the environment or additional anatomical sites such as the perineum or the hands, where residence is usually transient. Apparently, S. aureus is capable of a precise and balanced interaction with specific types of eukaryotic nasal cells. Although a wide variety of important bacterial ligands and possible eukaryote receptors have been described, the precise mechanisms leading to persistent bacterial colonization and, even more importantly, associated infection have not yet been elucidated in detail. This may be a consequence of the fact that most of the adherence factors have been studied individually in simplified in vitro systems, not taking the complexity of multi-factorial in vivo cell-cell interactions into account. An overall scheme of the initial and sequential interactions leading to S. aureus colonization of eukaryotic cell surfaces has not yet emerged. This review concisely describes the current state of affairs in the multi-disciplinary field of staphylococcal adherence research. Specific emphasis is placed upon the pros and cons of the various artificial, mostly in vitro models employed to study the interaction between bacterial and human or animal cells.

Affinity of Staphylococcus epidermidis to various prosthetic graft materials

BACKGROUND

Abdominal wall hernias have always been a major problem for general surgeons. The techniques of repairing primary, recurrent, and incisional hernias have evolved throughout the years at an accelerating trend, especially after production of prosthetic graft materials. Although looked upon with suspicion due to infection, fistula formation, and foreign body reaction, prosthetic graft materials are used deliberately in primary and recurrent hernias. The present study was designed to evaluate bacterial adherence to frequently used prosthetic graft materials.

MATERIALS AND METHODS

The study was carried out in five different groups with each group consisting of 10 identical samples of the same kind of prosthetic graft material. The prosthetic graft materials used in the study were polypropylene, polyglactin 910, polyester fibers, steel, and polytetrafluoroethylene (PTFE). These prosthetic graft materials were incubated in vitro with a Staphylococcus epidermidis strain which was ++++ adhesion positive. The degree of adhesion of S. epidermidis to prosthetic graft materials was assessed by the ELISA method.

RESULTS

Vicryl grafts showed significantly minimal bacterial adhesion whereas PTFE grafts tended to have more adhesion but this did not reach a statistical significance. Other graft materials did not show any difference for bacterial adhesion (Table 3).

CONCLUSION

These results suggest that in vitro S. epidermidis adhesion to Vicryl grafts is less than other types of prosthetic graft materials (P < 0.05 for all comparisons). Further in vitro and in vivo studies are required to confirm these results and to understand the complex interactions among bacteria, graft material, microenvironment, and surgical technique.

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.

Local application of vancomycin for prophylaxis of graft infection: release of vancomycin from antibiotic-bonded Dacron grafts, toxicity in endothelial cell culture, and efficacy against graft infection in an animal model

Methicillin-resistant strains of Staphylococcus epidermidis cause an increasing number of prosthetic infections. This prompted us to test the uptake of vancomycin in various graft materials in vitro, its influence on graft healing, and its efficacy against graft infection in pigs. Incubation of six different Dacron graft materials in a vancomycin solution (20 gm/L) was performed. Grafts were then placed in plasma, and samples were taken over 72 hours to determine vancomycin levels. Release of vancomycin ranged from 775 micrograms/cm2 to 3691 micrograms/cm2 after 1 hour of incubation. Gelatin-covered grafts increased release of vancomycin fourfold when incubation time was extended to 24 hours: uncovered grafts or the collagen-covered graft did not. Graft healing was not complicated when a vancomycin-bonded, gelatin-impregnated Dacron graft was implanted to replace the common femoral artery in pigs. Four weeks after implantation, histologic examination revealed normal development of neointima and perigraft scar tissue in the vancomycin-treated (n = 4) and untreated (n = 5) grafts. To test the efficacy of local vancomycin against graft infection, grafts were implanted in the groin of pigs and contaminated with 2 x 10(7) colony-forming units of Staphylococcus aureus. Four weeks after implantation, all grafts were infected in the untreated group (n = 6), with abscess, nonincorporated graft, and detection of S. aureus from the graft. In the treatment group (n = 6) vancomycin was added to the contaminated grafts. As a carrier for the vancomycin, we used a resorbable gelatin-glycerol foam. All grafts healed without infection. The difference between the treated and untreated groups is statistically significant (p < 0.05). We conclude that it may be effective to prevent graft infection with local application of vancomycin if an in situ replacement of infected graft (infected by gram-positive bacteria) is necessary or if there is a high risk of infection by methicillin-resistant- staphylococci.

Adhesion of Staphylococcus epidermidis to biomedical polymers: contributions of surface thermodynamics and hemodynamic shear conditions

Adhesion studies of Staphylococcus epidermidis RP62A were conducted using a rotating disk system to determine the roles of surface physicochemistry and topographies under physiologic shear conditions. Six materials were investigated: biomedical reference polyethylene and polydimethylsiloxane; argon plasma-treated reference polyethylene (Ar-PE); Silastic; expanded polytetrafluoroethylene; and woven Dacron. All of the polymers except Dacron demonstrated reduced bacterial adhesion with increasing shear stress. Argon plasma treatment of polyethylene reduced the level of staphylococcal adhesion. Adsorption of human plasma proteins effected significantly lower numbers of adherent bacteria. The lowest adhesion was observed for Ar-PE in 1% human plasma protein solution, whereas Dacron had the highest number of adherent bacteria. The high adhesion on Dacron was attributed to increased bacterial flux caused by topography-induced turbulent flow and physical entrapment of the bacteria in the fiber interstices. The results indicate that the driving force for S. epidermidis adhesion is strongly influenced by substrate physicochemistry, but this may be dominated by physical forces such as shear and turbulence.

Sterilisation of implantable devices

The pathogenesis and rates of infection associated with the use of a wide variety of implantable devices are described. The multi-factorial nature of post-operative periprosthetic infection is outlined and the role of sterilisation of devices is explained. The resistance of bacterial spores is highlighted as a problem and a full description is given of the processes of sterilisation by heat, steam, ethylene oxide, low temperature steam and formaldehyde, ionising radiation and liquid glutaraldehyde. Sterility assurance and validation are discussed in the context of biological indicators and physical/chemical indicators. Adverse effects upon the material composition of devices and problems of process control are listed. Finally, possible optimisations of the ethylene oxide process and their potential significance to the field of sterilisation of implants is explored.

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.

Polytetrafluoroethylene as an interpositional graft material for the correction of lower eyelid retraction

Polytetrafluoroethylene (PTFE), a nonantigenic, autoclavable, inert, woven synthetic graft material was used to correct ten lower eyelids with retraction secondary to either thyroid disease (7 eyelids) or surgically repaired maxillofacial trauma (3 eyelids). The material was well tolerated for postoperative periods ranging from 10 to 26 months. In two eyelids, a portion of the PTFE was removed to treat eyelid thickening and an infected meibomian gland. Results of histopathologic examination of the graft showed minimal inflammation and capillary and connective ingrowth into the graft matrix as well as a dense fibrous capsule around the graft. In selected cases, PTFE may be an acceptable substitute for other graft materials used in oculoplastic surgery.

Prospective randomized trial of polytetrafluoroethylene and Dacron aortic prosthesis. I. Perioperative results

Over a two year period 80 patients were entered into a prospective randomized trial comparing polytetrafluoroethylene (PTFE) and Dacron infrarenal aortic reconstructions. Fifty-four patients were treated for aneurysm (30 single tubed grafts; 24 bifurcation grafts), and 26 patients were treated for occlusive disease (26 bifurcation grafts). The groups were matched for age, sex and preoperative risk factors. Five patients died after operation (6.3%) including two from hemorrhage, but there were no significant differences in mortality and morbidity between the PTFE and Dacron groups. The volume of blood lost at operation (1930 +/- 1340 ml, all patients); the volume of blood transfused (2.98 +/- 2.43 units); the volume of crystalloids infused (3050 +/- 1390 ml); the intraoperative heparin dosage (67.9 +/- 20.5 mg); the clamp time (71.6 +/- 34.5 min); and the total operating time (228.1 +/- 78.3 min) also showed no significant differences between PTFE and Dacron. The ankle systolic pressure index rose more for PTFE (0.96 +/- 0.24) than for Dacron (0.82 +/- 0.20; P less than 0.002) at the time of discharge. This partially reflects a difference in the index between the groups before operation (PTFE 0.79 +/- 0.30; Dacron 0.72 +/- 0.32), but it may also indicate that PTFE is less thrombogenic than Dacron.

Review: Microbial colonization of prosthetic devices

The threat of bacterial colonization and biofilm formation poses the most important limitation on the use and development of prosthetic devices in human medicine. Data from the literature suggest that microbial adherence effected by the glycocalyx is a fundamental factor in sepsis involving biomaterials and that it may explain the resistance of such infections to host defense mechanisms and to antibiotherapy. A full appreciation of the existence and the consequences of the biofilm mode of bacterial growth is required so that we can both prevent and eliminate these protected microbial reservoirs.

Infections and prosthetic devices

Hundreds of thousands of people have temporary or permanent prosthetic devices inserted each year in the United States. Infection rates associated with these devices vary depending upon numerous factors; however, overall, several percent of these devices become associated with infection. Diagnosis of these infections can be complicated by underlying disease, surgery, or the prosthesis itself, making it difficult to ascertain whether abnormalities of routine diagnostic studies are caused by infection. Specific diagnostic tests are usually required to confirm the presence of infection and identify the causative organism. The frequent isolation of skin organisms (such as Staphylococcus epidermidis) as the pathogen can also cause confusion as to whether the culture was contaminated. Fortunately, treatment of these infections is usually successful, although removal of the prosthetic device is often necessary. Recent laboratory and clinical studies that demonstrate various steps in the development of these infections and their response to treatment will help to better determine the optimal prevention, diagnosis, and treatment of these infections.

Adhesion of coagulase-negative staphylococci to methacrylate polymers and copolymers

Adhesion of coagulase-negative staphylococci (CNS) was studied onto a homologous series of methacrylate polymers and copolymers. The materials varied in wettability (contact angles) and were either positively or negatively charged (zeta-potential). Bacterial adhesion experiments performed in a parallel-plate perfusion system showed that positively charged TMAEMA-Cl copolymers significantly promoted the adhesion of CNS as compared with all other methacrylate (co)polymers tested. The bacterial adhesion rates onto the positively charged surfaces are diffusion-controlled, whereas those onto the surfaces with a negative zeta-potential are more surface-reaction-controlled due to the presence of a potential energy barrier. The bacterial adhesion rates onto various poly (alkyl methacrylates) were similar. The number of adhering bacteria onto the negatively charged MMA/MAA copolymer did not differ from that onto pMMA, indicating that sufficient sites on the copolymer surface with the same potential energy barrier as that on pMMA, were available for adhesion. Decreasing rates of adhesion of CNS were observed onto MMA/HEMA copolymers with increasing HEMA content coinciding with increasing hydrophilicity. Low plateau values for the bacterial adhesion were observed on 50MMA/50HEMA, pHEMA, and 85HEMA/15MAA, indicating that the adhesion onto these materials was reversible. Four CNS strains with different surface characteristics all showed higher numbers of adhering bacteria onto 85MMA/15TMAEMA-Cl than onto 85MMA/15MAA and pMMA.

Bacterial adherence to vascular grafts after in vitro bacteremia

All currently used arterial prosthetics have a greater susceptibility to infection following bacteremia than does autogenous tissue. This experiment compares quantitative bacterial adherence to various prosthetic materials after bacteremia carried out in a tightly controlled and quantitative fashion. Ten centimeters long, 4 mm i.d. Dacron, umbilical vein (HUV), and polytetrafluoroethylene (PTFE) grafts, as well as PTFE grafts with a running suture line at the midportion were tested. Each graft was interposed into a pulsatile perfusion system modified from a Waters MOX 100 TM renal transplant pump. Indium-111-labeled Staphylococcus aureus were added to heparinized canine blood to give a mean concentration of 4.7 X 10(6) bacteria/cc. This infected blood was recirculated through each graft for 30 min at a rate of 125 cc/m, 100 Torr (sys), 60 beats/min. The gamma counts/graft were used to calculate the number of bacteria/cm2 of graft surface. After nine experiments, a mean of 9.63 X 10(5) bacteria/cm2 were adherent to the Dacron, 1.04 X 10(5) bacteria/cm2 to the HUV, and 2.15 X 10(4) bacteria/cm2 to the PTFE. These differences were all significant at the 0.05 level. The addition of a suture line increased bacterial adherence to the PTFE graft by 50%. These results suggest that PTFE is the vascular graft material of choice when a prosthetic graft must be implanted despite a high risk of subsequent clinical bacteremia. Our in vitro, pulsatile perfusion model gave accurate and reproducible results, and appears well suited for further studies of bacterial, or platelet adherence to grafts, as well as the biomechanics of vascular conduits.

A model of catheter colonisation in vitro and its relationship to clinical catheter infections

A laboratory model for colonisation of silicone-rubber catheters by staphylococci is described. The criteria for true colonisation that involves adhesion of the organisms to the luminal surface are discussed. Light and scanning electron micrographs of the microcolonies produced in the laboratory model suggest that the same mechanisms of adhesion, involving extracellular slime, apply as in clinically colonised catheters. Potential uses of the model, for studying further the mechanisms of colonisation and particularly its prevention and treatment, are discussed.

Attachment of staphylococci to various synthetic polymers

Attachment of staphylococci to different synthetic polymers used for medical purposes was studied in applying the bioluminescent technique. The number of attached bacterial cells was determined by measuring the light emission resulting from the reaction between firefly luciferase and ATP present in adhered staphylococcal cells. It was shown that staphylococci attach to synthetic polymers within a few minutes, although one hour incubation is required to reach a constant maximum value of attached cells. Ten different synthetic polymers and five Staphyloccocus epidermidis strains were investigated in our study. The relationship between surface properties of polymers and bacterial attachment was studied. Various physicochemical parameters of synthetic polymers and bacteria were determined (contact angle, surface tension). It was demonstrated that bacterial attachment decreases with decreasing contact angle and with increasing surface tension of synthetic materials. Modifications of surface charge and hydrophobicity of solid materials were also investigated. It could be proved that especially negatively charged and hydrophilic synthetic polymers show very decreased staphylococcal attachment.

Examination of the morphology of bacteria adhering to peritoneal dialysis catheters by scanning and transmission electron microscopy

We examined Tenckhoff peritoneal catheters by scanning and transmission electron microscopy to study the morphology of bacterial adherence. Two catheters were removed from uninfected patients, three from patients with exit site infections, four from patients with peritonitis, and one from a patient with both exit site infection and peritonitis. Infecting organisms included three of Staphylococcus aureus and one each of Enterobacter sp., Staphylococcus epidermidis, Achromobacter xylosoxidans, Serratia sp., Klebsiella sp., and Candida albicans. Considerable morphological variation in adherence to the peritoneal dialysis apparatus occurred. No inflammatory cells were ever seen in association with infected cuffs, only two of the five patients with peritonitis had inflammatory cells associated with their catheters. In both instances, these cells tended to occur in clumps and demonstrated no flattening when in contact with the surface. Colonization of the catheter was uneven--bacteria tended to occur in clusters. Extensive matrix formation was evident in several instances, and condensation of this matrix onto the bacteria during the dehydration process rendered clumps of bacterial cells amorphous at times. Bacteria were adherent to the subcutaneous cuff in those patients with exit site infections. Gram-negative bacteria attached to individual dacron fibers of the cuff, often several layers deep. Gram-positive bacteria tended to adhere in clusters.