J. P. Guggenbichler

A new technology of microdispersed silver in polyurethane induces antimicrobial activity in central venous catheters

SummaryMetal ions or metal ions in complexes or compounds have been used for centuries to disinfect fluids, solids and tissues. The biocidal effect of silver, with its broad spectrum of activity including bacterial, fungal and viral agents, is particularly well known and the term “oligodynamic activity” was coined for this phenomenon. Silver ions have an affinity to sulfhydryl groups in enzyme systems of the cell wall, through which they interfere with the transmembranous energy transfer and electron transport of bacterial microorganisms. Silver ions also block the respiratory chain of microorganisms reversibly in low concentrations and irreversibly in higher concentrations. Binding to the DNA of bacteria and fungi increases the stability of the bacterial double helix and thus inhibits proliferation. There is no cross resistance with antibiotics and also no induction of antimicrobial resistance by silver ions. The concentrations required for bactericidal activity are in the range 10−9 mol/l. These concentrations can be achieved in solution by the interaction of metallic silver with electrolytes only if there is a large enough surface of silver. By a novel technology, metallic silver is distributed in submicron particles in polyurethane and results in a concentration of 0.8% in an active surface of 450 cm2/g polyurethane. Polyurethane is hygroscopic and rapidly attracts water; the interaction of electrolyte solutions with the extremely finely distributed silver throughout the polyurethane releases bactericidal concentrations of silver ions over a period of years to the surface of the material. The electronegatively charged surface of bacteria attracts the positively charged silver ions. The concentrations released from the polyurethane are far below the toxic concentrations for humans.

A new method for screening anti-infective biomaterials

Implantable medical devices such as catheters are indispensable in the management of critically and chronically ill patients for the administration of electrolytes, drugs, parenteral nutrients, blood components or drainage of secretions and pus. Artificial heart valves, prosthetics, ceramics, metals and bone cements are standard implants. All of these implants save human lives and enhance quality of life. At the same time they are the leading cause for millions of primary nosocomial bloodstream infections with substantial morbidity and mortality. A property common to all these biomaterials is the ease by which they are colonized by pathogenic and nonpathogenic microorganisms, often requiring immediate removal. Several methods have been devised to decrease the risk of foreign body-associated infections. These include the use of meticulous hygienic precautions, the development of hydrophilic materials to minimize bacterial adhesion and impregnation with antiseptics and antibiotics. Silver, in particular free silver ions, is well known for its powerful and broad–spectrum antimicrobial activity still allowing the independent use of therapeutic antibiotics. The investigation of the antimicrobial activity of implants containing silver as an antimicrobial agent is difficult because many silver compounds are poorly water soluble, resulting in low concentrations of silver ions released into the surrounding medium. Therefore, the antimicrobial efficacy of polymers impregnated with elementary silver cannot be tested by routine agar diffusion measurements. Like other procedures, the agar diffusion technique was also inappropriate for a simultaneous highthroughput screening of silver prototypes. Reliable in vitro methods for antimicrobial activity testing of surfaces are essential for the development of new anti-infective biomaterials. Cell proliferation is an important step in the course of infection and must be included in any evaluation procedure. To date, assays have focused on the monitoring of bacterial adherence but lack an analysis of the microbial proliferatory behavior. For a precise testing of antimicrobial efficacy three independent aspects must be considered: adhesion (the test must detect and quantify adherent microorganisms); proliferation (the test should assay the potential of adherent bacteria for proliferation); and detection of bactericidal and bacteriostatic activity. Here, we introduce a new technique for testing antimicrobial properties of biomaterials using a microplate system (Fig. 1). As a selected example, we show in vitro data for the antimicrobial activity of silver polymers, which correlate positively with multicenter clinical trials. Implications of the approach. The number of new biomaterials in medicine is steadily growing. Highly efficient in vitro methods are required for quality control, screening and product improvement. Such comparative techniques should meet the following requirements: a quantification method to monitor microbial adherence; a sensitive and reproducible detection of antimicrobial activities in a proliferation assay reflecting dose/response relationships; parallel screening of a set of biomaterials in a high-throughput analysis; exposure of only well-defined surface areas; and positive correlation with clinical data. The microplate-comb model method fulfills all these requirements. A prominent feature is that it is easily standardized. It can also be used to investigate influences of geometry and microstructure of surfaces, the binding behavior of surfaces in response to cells, agents, coatings and surface-active compounds or protective protein layers. Analytical tools such as ELISA, enzyme-linked lectin sorbent assay (ELLA), colorimetric and fluorescent assays are compatible with the microplate-comb model technology. The broad spectrum of possible applications and modifications reflects the assay’s high versatility.

The Erlanger silver catheter: in vitro results for antimicrobial activity.

SummaryThe antimicrobial activity of a silver-impregnated polymer catheter (the Erlanger silver catheter) was demonstrated by determining the microbial adhesion to the surface of the catheter and by measuring the rate of proliferation (viability) of microorganisms at this site. On the surface of a catheter impregnated with silver, according to previously described methods, the bacterial adhesion ofStaphylococcus epidermidis is reduced by 28–40%. Bacterial proliferation on the surface of the catheter and biofilm production are also substantially reduced by the elution of free silver ions from the catheter matrix. Bacteriostatic and bactericidal activities can be determined. The antimicrobial efficacy of the silver catheter is not reduced by blood components. There is no loss in antimicrobial activity for weeks after preincubation in water or phosphate buffered saline. The antimicrobial activity depends on the extent of the active silver surface.

Antimicrobial activity and biocompatibility of polyurethane and silicone catheters containing low concentrations of Silver: A new perspective in prevention of polymer-associated foreign-body-infections

In modern medicine, infection is one of the most serious complications of implanted plastic devices. The host is not able to overcome this special type of opportunistic infection despite having a normal immune response and a low virulence of most of the bacteria involved. Antimicrobial therapy alone generally cannot cure the infection and the removal of catheters often remains the only choice of therapy. Bacterial adhesion to the polymer surface of the catheter, be it luminal or external, is an important step in the pathogenesis of catheter-associated infections. In this report, we describe new approaches to the prevention of infections by impregnation of polyurethane and silicone with silver by two different methods. The antimicrobial activity of these silver-impregnated catheters is more than 10 fold higher for coagulase-negative staphylococci (CNS) compared to catheters without silver. Similar results are obtained with other microbial organisms like Staphylococcus aureus, Enterococcus faecalis, Escherichia coli, Pseudomonas aeruginosa and Candida albicans. The new polymers show no cytotoxic or thrombogenic side effects in vitro.

Biocompatibility testing of a new silver-impregnated catheterin vivo

SummaryThe purpose of this investigation was to compare the local effects of polyurethane (Tecothane®) and silicone tubes with or without silver impregnation in rats. Bacterial colonization or infection of the exit site and/or tunnel were documented and interpreted. All tubes were placed subcutaneously or percutaneously in the neck of 41 Sprague-Dawley rats and guided beneath the dorsal muscles into the peritoneal cavity. The incidence of bacterial abscesses along the implanted tubes was evaluated daily. After 90 days, or earlier if sepsis developed, the animals were killed painlessly and various organs and tissues from the entry site and the catheter tunnel examined histologically. In the group where polyurethane tubes were placed percutaneously, there was no difference in the frequency of abscesses between silver-impregnated and non-impregnated tubes (5/6 with and 5/7 without silver). The only difference noted was in the group with percutaneously placed silicone tubes between those with and without silver. Abscesses only occurred in 2/4 animals in the silver group and in 5/5 animals in the control group. Histological examination showed no difference in either group between infectious and foreign body reactions. Silver particles in subcutaneous, muscle and peritoneal tissue could not be demonstrated.

Analysis of the acute cytotoxicity of the erlanger silver catheter

SummaryThe Erlanger silver catheter consists of a new form of polyurethane, which contains finely dispersed metallic silver. The aim of this study was to establish the biocompatibility of this intravenous catheter by investigating the acute cytotoxicity of extracts from the Erlanger silver catheter on human fibroblasts and lymphocytes. Extracts of the Erlanger silver catheter were not cytotoxic for MRC-5 human fibroblasts nor for sensitized phytohem-agglutinin (PHA)-stimulated human lymphocytes. The addition of silver powder of up to 2% by weight to the basic catheter polyurethane TecothaneTM led to no increase in acute cytotoxicity in comparison with untreated TecothaneTM. The Erlanger silver catheter is a new intravenous catheter with good biocompatibility.

Thrombogenicity testing of central venous cathetersin vitro

SummaryTo date there have been no standard methods for assessing the thrombogenicity of central venous catheters. A procedure for testing the thrombogenicity of intravenous lines such as the silver-impregnated catheter by continuous blood flowin vitro was therefore developed. For this test, fresh blood was drawn from healthy human donors and anticoagulated with sodium citrate (1∶9). All material tested (catheter tubes with and without silver manufactured in the same way, polyethylene tubes and tubes with potentially thrombogenic material) were perfused through their lumen with anticoagulated blood for up to 31 hours. Blood samples were collected at different times from the test system at sites before and after the perfusion of the test catheters. The hemoglobin concentration, erythrocyte, leukocyte and thrombocyte counts and markers for thrombin activation (thrombinantithrombin III-complex, F1+2-prothrombin fragments) and for hyperfibrinolysis (d-dimers) were determined. No thrombin activation or signs of hyperfibrinolysis were detected in any material tested. Polyethylene tubes were found to cause hemolysis, as shown by a decrease in hemoglobin content from 15 g% to 4.5 g%. Tecothane® tubes with and without silver did not induce hemolysis.

Experience with the use of piperacillin–tazobactam in pediatric non-renal solid organ transplantation

Abstract:  Bacterial infection remains a major problem after solid organ transplantation (SOT), especially in children. Piperacillin–tazobactam (Pip–Tazo) is a beta‐lactam‐antibiotic combination with a broad spectrum of activity including gram‐positive cocci as well as gram‐negative rods, non‐fermentative and anaerobic bacteria. The aim of this retrospective study was to critically review our experience with Pip–Tazo as perioperative prophylactic agent in pediatric non‐renal SOT. Between 1993 and 2003 Pip–Tazo was used as initial perioperative prophylaxis in 45 pediatric patients who underwent a total of 49 transplants (36 liver‐, seven cardiac‐, two lung‐, and four small bowel‐) at our department. Median age of the children was 7.9 (range 0.5–18.1) years. A total of 34 rejection episodes following 27 transplants were diagnosed. During first hospitalization 44 infectious episodes were observed. Bacteria were responsible for 22 episodes including sepsis (n = 10), pneumonia (n = 5), wound infection (n = 4), urinary tract infection (n = 1), and clostridial colitis (n = 2). The isolated organisms were gram‐positive cocci (n = 12), gram‐negative rods (n = 3), non‐fermentative bacilli (n = 4), and anaerobes (n = 3). Ten episodes were caused by Pip–Tazo resistant bacteria. Twenty‐one of these infections were observed following antirejection therapy with pulse steroids. At later time points nine infectious episodes were successfully treated with a second course of Pip–Tazo. During follow up, eight patients died. Six deceased perioperatively: five from infection including aspergillosis (n = 4) and Pneumocystis jiroveci pneumonia (n = 1) and cerebrovascular bleeding (n = 1) and two children later on. At present 37 children (82%) are alive with well functioning graft after a median follow up of 39.2 (range 0.6–123.5) months. No severe side effects caused by Pip–Tazo were observed in any of the children. Pip–Tazo may be a suitable single agent for perioperative prophylaxis in pediatric non‐renal solid organs recipients, however, a prospective comparative study is needed to make final conclusions.

Silver catheter study: Methods and results of microbiological investigations

SummaryWithin the framework of the clinical study of the Erlangen silver catheter 104 silver catheters and 105 control catheters were tested by microbiological culture. This was done by rolling the catheter on a blood agar plate, washing the lumen through with tryptic soy broth (TSB) and, after ultrasound treatment, incubating the catheter tip in TSB as an enrichment culture for detecting very low bacterial counts. There was good agreement in the numbers of colony-forming units (CFU) detected by the roll plate and luminal washout cultures in 92% of the silver and 89% of the control catheters tested. Seventy-six (73%) of the 104 silver catheters showed no bacterial growth and 16 (15%) showed very low bacteria counts (<15 CFU), or growth only after enrichment, which were attributed in both instances to catheter contamination. Twelve catheter tips (12%) showed significant bacterial counts greater than 15 CFU which were indicative of colonization or catheter-related infection. Corresponding results in the control catheters were 59 (56%), 28 (27%) and 18 (17%), respectively, a higher rate of infection or contamination which was stastistically significant (chi-square test: P=0.04).

Clinical study of the erlanger silver catheter—Data management and biometry

SummaryThe clinical evaluation of venous catheters for catheter-induced infections must conform to a strict biometric methodology. The statistical planning of the study (target population, design, degree of blinding), data management (database design, definition of variables, coding), quality assurance (data inspection at several levels) and the biometric evaluation of the Erlanger silver catheter project are described. The three-step data flow included: 1) primary data from the hospital, 2) relational database, 3) files accessible for statistical evaluation. Two different statistical models were compared: analyzing the first catheter only of a patient in the analysis (independent data) and analyzing several catheters from the same patient (dependent data) by means of the generalized estimating equations (GEE) method. The main result of the study was based on the comparison of both statistical models.