Medullary osteogenesis with platinum cathodes

Studies of electrical stimulation of osteogenesis with stainless steel electrodes have previously established a dose-response relationship between current and bone growth. Examination of the effect of differing geometric current densities resulted in the conclusion that very little electrode surface area was involved in stimulation and led to the design of a multiport "distributive" cathode. A series of experiments were performed to extend these results to wire and multiport platinum electrodes. As before, a current-bone growth dose-response relationship was found. Peak bone growth was greater than for stainless steel. However, peak bone growth occurred at 2.0 microA (versus 20 microA for stainless steel). Correlation studies suggest that small changes in cathodic potential affect bone growth more than similar size changes in current. Finally, the generally benign local host response to platinum suggests that platinum may be a suitable material for chronic indwelling anodes for stimulation of osteogenesis.     

Bacterial colonization of intravenous catheter materials in vitro and in vivo

Four different intravenous catheter materials, brands Teflon, Silastic, Vialon, and Tecoflex, were evaluated in vitro for bacterial adherence after 2 and 24 hours' incubation in trypticase soy broth and after 2 hours' incubation in nutrient-free phosphate buffer (pH 7.2). The organisms used were Pseudomonas aeruginosa, Enterobacter aerogenes, Escherichia coli, and Staphylococcus epidermidis. The significant differences in in vitro adherence of the different bacterial species to the various catheters were then evaluated in vivo by intravenous injection of a single bolus of 1 X 10(5) organisms via tail vein of rats with previously placed catheters in their superior venae cavae. There was no association between the in vitro bacterial adherence and the tendency of the in vivo catheters to become colonized. Results of scanning electron microscopy of clean catheters and those removed from the rats showed obvious differences in surface characteristics and in clot adhesion between the catheters. These characteristics did not correlate with bacterial adherence in vitro or colonization in vivo. It is concluded that laboratory studies of bacterial adherence to, physical characteristics of, and thrombogenicity of intravenous catheters do not necessarily translate into resistance to clinical catheter sepsis.     

In vitro quantitative adherence of bacteria to intravascular catheters

Adapting standard techniques, a simple in vitro system was devised to compare quantitative bacterial adherence to iv catheters of different compositions. Upon brief immersion of catheters in suspensions of Staphylococcus aureus, coagulase-negative staphylococci, and Escherichia coli, organisms adhered to catheter surfaces. After overnight growth in broth, organisms remained adherent and formed colonies, as shown by light and scanning electron microscopy. In addition, quantitative adherence using a blood agar roll technique, expressed as bacteria per square centimeter of catheter surface area per 10(6) colonies per milliliter inoculum, was calculated. Adherence was greater on polyvinylchloride (PVC) catheters (geometric mean 342) than on Teflon catheters (geometric mean 49.6) for coagulase-negative staphylococci (P less than 0.005). Also, the number of coagulase-negative staphylococci adherent to PVC catheters was significantly greater than for E. coli (geometric mean 70.6) at analogous inocula (P less than 0.02). Differences in bacterial adherence to the surface of iv devices may be important in the pathogenesis of catheter-associated infections. This in vitro method could prove useful in testing bacterial adherence properties of newly developed catheter materials, and allow development of catheters less prone to be associated with bacterial adherence and catheter-related infections.     

Bacterial adherence to tantalum versus commonly used orthopedic metallic implant materials

OBJECTIVES: Evaluation of bacterial adhesion to pure tantalum and tantalum-coated stainless steel versus commercially pure titanium, titanium alloy (Ti-6Al-4V), and grit-blasted and polished stainless steel. DESIGN: Experimental in vitro cell culture study using Staphylococcus aureus and Staphylococcus epidermidis to evaluate qualitatively and quantitatively bacterial adherence to metallic implants. METHODS: A bacterial adhesion assay was performed by culturing S. aureus (ATCC 6538) and S. epidermidis (clinical isolate) for one hour with tantalum, tantalum-coated stainless steel, titanium, titanium alloy, grit-blasted and polished stainless steel metallic implant discs. Adhered living and dead bacteria were stained using a 2-color fluorescence assay. Adherence was then quantitatively evaluated by fluorescence microscopy and digital image processing. Qualitative adherence of the bacteria was analyzed with a scanning electron microscope. The quantitative data were related to the implant surface roughness (Pa-value) as measured by confocal laser scanning microscopy. RESULTS: Bacterial adherence of S. aureus varied significantly (p = 0.0035) with the type of metallic implant. Pure tantalum presented with significantly (p < 0.05) lower S. aureus adhesion compared to titanium alloy, polished stainless steel, and tantalum-coated stainless steel. Furthermore, pure tantalum had a lower, though not significantly, adhesion than commercially pure titanium and grit-blasted stainless steel. Additionally, there was a significantly higher S. aureus adherence to titanium alloy than to commercially pure titanium (p = 0.014). S. epidermidis adherence was not significantly different among the tested materials. There was no statistically significant correlation between bacterial adherence and surface roughness of the tested implants. CONCLUSIONS: Pure tantalum presents with a lower or similar S. aureus and S. epidermidis adhesion when compared with commonly used materials in orthopedic implants. CLINICAL IMPLICATION: Because bacterial adhesion is an important predisposing factor in the development of clinical implant infection, tantalum may offer benefits as an adjunct or alternative material compared with current materials commonly used for orthopedic implants.     

Uropathogenic Escherichia coli-induced neutrophil adhesion to urinary epithelium is strain-specific and mediated by CD11b/CD18

Adherence of Escherichia coli to urinary tract epithelium induces neutrophil migration across the uroepithelium to combat bacterial infection. Neutrophil adherence to the apical membrane of uroepithelial cells may be an important factor for bacterial clearance. We used an in vitro model of urinary tract infection to examine the effects of uropathogenic E. coli on neutrophil adhesion to the uroepithelial cell line RT4. We found that distinct clinical isolates caused different levels of neutrophil adherence. One particular isolate caused significant neutrophil adhesion in a dose- and time-dependent manner. The neutrophil adhesion-promoting effect induced by this isolate was not caused by bacterial secreted products, suggesting that contact between intact E. coli and uroepithelial cells is required for promoting neutrophil adhesion. This adhesion was almost exclusively mediated by CD11b/CD18, suggesting that E. coli upregulates CD11b/CD18 counterligands on the uroepithelial surface. These data suggest that certain uropathogenic E. coli selectively promote adhesion of neutrophils to ligands on uroepithelial cells by a CD11b/CD18-dependent mechanism. Received: 27 October 2000 / Accepted: 27 December 2000     

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.     

Influence of Oxynitrided Surface in the Production of a Less Susceptible Titanium Surface to Skin‐Borne Bacterial Adhesion

There is a growing quest for an ideal biomaterial that shows appropriate cellular response and is not susceptible to microbial adhesion. In this study, commercial grade II titanium was submitted to RF/DC plasma surface modification at 2.2 mbar, using gas mixtures of argon, nitrogen, and oxygen at proportions 4:1:2 and 4:1:3. The surfaces were physically and chemically characterized. In order to evaluate bacterial response, the surfaces were exposed to Staphylococcus epidermidis. Oxynitrided samples, although having a higher roughness as compared with untreated samples, exhibited lower bacterial growth. This observation is probably due to the formation of different crystalline phases of nitrides and oxides caused by plasma treatment. The surface with highest contact angle and highest surface tension showed lower bacterial adhesion. These results were confirmed by scanning electron microscopy. The role of nitrogen in reducing bacterial adhesion is clear when this material is compared with untreated titanium, on which only an oxide film is present.     

Bacterial adhesion to surfactant-modified silicone surfaces

OBJECTIVE: Ventricular shunt infections are a major contributor to morbidity in patients being treated for hydrocephalus. The majority of these infections are from Staphylococcus epidermidis. Prevention of bacterial adhesion to the silicone surface of a ventricular catheter could decrease shunt infections. We studied the effectiveness of a surfactant and/or 2% iodine prewash on preventing bacterial adhesion to Silastic catheter material. METHODS: In a laboratory setting, various concentrations of a surfactant, Poloxamer-188 (P188), and a bactericidal agent, iodine, were compared against a control solution in their ability to prevent bacterial adhesion of S. epidermidis to a silicone surface. Silicone wafers were soaked for 1 hour in the test solution, then inoculated and incubated with S. epidermidis for 24 hours. Bacterial counts were then obtained and compared. RESULTS: The most effective method tested in this study was 20% P188, which allowed only 3.02% bacterial adhesion compared with 22.2% bacterial adhesion in the control (P < 0.001). P188 at a 10% concentration or 20% mixed with iodine had the next most effective inhibition. Of the germicidal solutions, a 5-ppm solution of iodine was the most effective. The most ineffective method tested was 2 ppm iodine, which allowed 13.2% bacterial adhesion. CONCLUSION: Use of a surfactant and/or a germicidal will provide some protection against bacteria attaching to silicone surfaces before they are surgically implanted. The use of a surfactant soak of 20% P188 or iodine at a concentration of 5 ppm before inoculation with S. epidermidis significantly decreased the bacterial adhesion to silicone wafers. This finding has relevance to clinical practice because it highlights a simple step undertaken before implanting a ventricular catheter that could reduce the adhesion rate of the most common contaminant of these catheters. This step may become an important factor in decreasing infection rates in shunt-dependent patients.     

An electrified catheter to resist encrustation by Proteus mirabilis biofilm

PURPOSE: We investigated the effect of iontophoresis produced by passing an electric current through silver electrodes attached to catheters on catheter encrustation by crystalline Proteus mirabilis biofilm. MATERIALS AND METHODS: Four glass bladder models were catheterized with 16Fr silicone catheters, of which 3 had 0.25 mm silver wires running through and beside the lumen. Two wired catheters had the silver wires connected to a 9 V direct current source supplying a steady current of 150 microA via a self-regulating circuit. Artificial urine, which had been inoculated with a clinical strain of P. mirabilis isolated from an encrusted catheter, was instilled into the bladder model at 0.5 ml per minute. The models were operated until the test catheters became blocked. Mean blockage time was statistically analyzed by ANOVA. Bacterial colony count, silver ions and pH were assessed every 24 hours. RESULTS: The experiment was repeated 3 times. Time to blockage, colony count, pH and scanning electron microscopy was used to assess encrustation in electrified and control catheters. Time to blockage in electrified vs control catheters was 156 vs 22 hours. The difference in blockage times was statistically significant (p <0.002). The viable bacterial cell count in urine with test catheters vs that in controls was 1.12 x 10(4) vs 2.73 x 10(9) cfu/ml. The pH increased to 9 in control models, whereas it remained less than 6.5 in test models for about 100 hours. CONCLUSIONS: Electrified catheters released ions in urine that have the oligodynamic property of inhibiting bacterial growth. The application of electric current to catheters fitted with silver electrodes significantly decreased the rate at which these devices became encrusted by P. mirabilis. This principle could be used to prevent encrustation on long-term catheters.     

Factors predisposing to urinary tract infections in children

The normal urinary tract is sterile for many reasons. These include: bacterial eradication by urinary and mucus flow, urothelial bactericidal activity, urinary secretory IgA, and blood group antigens in secretions which interfere with bacterial adherence. Periodic emptying of the bladder should wash bacteria out, but uropathogens grow well in urine and their rapid doubling time might not clear bacteria by voiding at the usual frequency. The ability to colonize the gut, as well as adhere to host squamous and urothelial cells, is due to bacterial adherence, a mechanism by which fluid washout would not be effective. Fimbriae or pili, hair-like surface appendages of Escherichia coli, are the usual adhesins. E. coli with type 1 fimbriae adhere to mucus, and P-fimbriae adhere to glycolipids on mucous membranes and urothelial cells. Other common virulence factors of E. coli include the capsule, which prevents phagocytosis, hemolysin, which damages urothelium, and aerobactin, which sequesters iron. Adherence stimulates the inflammatory response by activation of cytokines such as interleukin-1, -6, and -8. These cytokines stimulate the production of intercellular adhesion molecule, which by leukocyte adhesion causes migration of these cells to the site of infection to counteract it. Received September 22, 1995; received in revised form January 22, 1996; accepted January 25, 1996     

Adherence of Staphylococcus aureus isolated in peritoneal dialysis-related exit-site infections to HEp-2 cells and silicone peritoneal catheter materials

Background. Peritoneal catheter exit-site infections cause a relevant morbidity in peritoneal dialysis patients and are frequently caused by Staphylococcus aureus. We tested the hypothesis that adherence of exit-site-derived S.aureus to epithelial cells and peritoneal catheter silicone tubes discriminates virulent and less virulent strains. Methods. The binding of isolated S. aureus to an epithelial cell line (HEp-2) and to silicone tubes was analyzed using light-microscopy or radioactive labeling of bacteria. Results. Of 378 exit-site swabs, 99% (26%) were positive for microbial growth. S. aureus was cultured in 25 of 99 positive swabs; three of 13 swabs taken in exit-site infections grade 3 and 4 that had tested positive for S. aureus. Adherence of S. aureus from exit-site infections grade 2, 3 and 4 to Hep-2 cells did not differ from adherence of bacteria isolated from asymptomatic or moderately inflamed catheter exit sites (grade 0-2). However, binding of S. aureus to silicone tubes was enhanced in grade 0/1 compared with grade 2-4 exit-site isolates. Conclusions. Staphylococcus aureus is an important pathogen in CAPD-related exit-site infection being isolated in about 6.6% of all exit-site swabs (and in 25% of all positive swabs). Silicone-adhesive strains may be of more clinical significance in peritoneal dialysis patients since adhesion to silicone was increased in S. aureus strains isolated in more severe exit-site infections.     

结核分枝杆菌对材料粘附能力的体外实验研究

目的：通过体外实验观察结核分枝杆菌对内植物材料的粘附情况，从细菌粘附角度出发探讨脊柱结核内固定术的安全性问题，方法：以表皮葡萄球菌为对照，在表皮葡萄球菌、结核分枝杆菌菌液中分别加人不同材料，扫描电镜观察，比较不同细菌对不同材料(钛合金、不锈钢)、不同表面(光滑面、粗糙面)的粘附情况。结果：结核分枝杆菌对两种材料的粘附均较表皮葡萄球菌少，粗糙表面所粘附的细菌量较光滑面多。结论：结核分枝杆菌对内植物材料的低粘附性可能是临床脊柱结核内固定术安全的原因之一。     

人工关节假体不同材料及材料表面粗糙度对表皮葡萄球菌粘附能力的影响

目的探讨人工关节假体材料及表面粗糙度对表皮葡萄球菌粘附能力的影响。方法制作超高分子聚乙烯、钛合金和钴铬钼合金试样，表皮葡萄球菌经FITC标记，人工关节材料试样消毒后接种FITC标记的表皮葡萄球菌，试样表面分为光滑表面和粗糙表面，每组各6个试样，将含有细菌和试样的24孔板在37℃下孵育30min后，用荧光显微镜观察，试样用扫描电镜观察。结果对于光滑的人工关节常用材料表面，表皮葡萄球菌对超高分子聚乙烯（UHMWPE）的粘附能力显著高于钛合金和钴铬钼合金（P〈0．001），对钴铬钼合金的粘附能力要高于钛合金（P〈0．05）；粗糙的超高分子聚乙烯和钴铬钼合金表面比光滑的表面更易引起表皮葡萄球菌的粘附（P〈0．01），而细菌对粗糙钛合金的粘附仅轻微高于光滑钛合金（P〉0．05）。荧光照相观察及扫描电镜观察显示细菌在粗糙表面的划痕内聚集粘附。结论本研究结果表明细菌对人工关节材料表面的粘附能力不但取决于细菌本身，也和材料性质和表面粗糙度有关。     

Effect of weak direct current with silver electrodes on bacterial growth

The author studied the effect of weak direct current on bacterial growth in vitro and in vivo. In vitro, electric current was applied 20 or 100 micro A/cm2 of direct current using electrode of carbon, silver or platinum. Its inhibitory effect was observed on the growth curve of Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa in the anode bath respectively. A silk thread that adsorbed Staphylococcus aureus was inserted into the intramedullary space of the tibia of Wistar rats to induce osteomyelitis. Silver electrodes were placed to apply 100 microA/cm2 of direct current for two weeks. The therapeutic effect was then evaluated in terms of X-ray findings, histological findings and changes in the viable count of Staphylococcus aureus in the intramedullary space of the tibia. It was found that application of electric current using a silver electrode was most effective for the inhibition of bacterial growth both in vivo and in vitro, and seemed to be clinically useful for treating osteomyelitis.     

Electrode-oxygen consumption and its effects on tissue-oxygen tension. A study by mass spectrometry

A theory for the mechanism of electrical bone stimulation proposes that passage of an electric current reduces the local PO2 and raises the pH near the cathode, thereby creating a favorable environment for osteogenesis. To study the effects of electric current passage on the PO2, PCO2 and pH in the vicinity of the electrodes in vivo, a wire electrode spiralled around the catheter of a clinical mass spectrometer was placed in dog muscle. Electrodes were made of stainless steel or platinum. With a cathode located in the tissue, a 20-microA direct constant current caused a drop in PO2 of 5-10 mmHg and a drop in PCO2 of 2-6 mmHg, both reaching plateaus again within five to 20 minutes. The time required to reach this new equilibrium was shorter for platinum than for stainless steel. When the electric current was turned off, PO2 and PCO2 reversed to their original values. Because of the high buffer capacity of tissue, it is highly unlikely that 20-microA current would induce a change in pH.     

Cell adhesion to biomaterials: correlations between surface charge, surface roughness, adsorbed protein, and cell morphology

Adhesion of cells to a biomaterial surface can be a major factor mediating its biocompatibility. In this investigation, jet impingement techniques were used to quantify strength of cellular adhesion to various material surfaces. The metals tested: HS25 (a cobalt-based alloy similar to F75), 316L stainless steel, Ti-6Al-4V, and commercially pure tantalum, exhibited nearly a fivefold increase in adhesion strength above that characteristic of the polymeric materials tested (PTFE, silicone rubber, and HDPE). The present study examines physical and biological factors that might influence fibroblast adhesion to the biomaterial surface. The relation between surface charge and cellular adhesion was investigated in a controlled manner by measuring adhesion strength over a range of charge densities. The cells showed charge and electrical potential-dependent adhesion maxima, suggesting that surface alloying for optimum adherence may be possible. In a preliminary series of experiments adsorbed serum protein layers on a series of materials of differing adherence were investigated using gel electrophoresis to assess protein composition. Analysis of adsorbed proteins revealed little difference in relative abundance or total adsorption quantity. SEM micrographs of cells on Ti-6Al-4V and silicone rubber (high and low adhesion materials, respectively) demonstrated differences in cell morphology and cell density.     

Bacterial adherence to plain and tobramycin-laden polymethylmethacrylate beads.

Antibiotic-impregnated polymethylmethacrylate (PMMA) bead chains are in current clinical use for prophylaxis and management of osteomyelitis. The in vivo interaction between PMMA beads and an experimentally infected wound is examined. Two modes of bacterial adherence to plain PMMA beads are demonstrated. In this report, tobramycin-sensitive bacteria did not attach to tobramycin-laden beads. Therefore, implanted PMMA beads should contain an antibiotic to which the infecting bacteria is sensitive.     

Why are Foley catheters so vulnerable to encrustation and blockage by crystalline bacterial biofilm?

Many patients undergoing long-term bladder catheterisation experience blockage and encrustation of their catheters. The problem stems from infection by urease producing bacteria, particularly Proteus mirabilis. Bacterial biofilms colonise the catheters, the activity of urease raises the pH and induces the deposition of calcium and magnesium phosphate crystals. In this study, a laboratory model of the catheterised bladder has been used to examine the early stages in the formation of the crystalline biofilms. The results show that initial cell adhesion is to the irregular surfaces surrounding the catheter eye-holes. Microcolonies form in depressions in these surfaces and spread to cover the entire surface of the rims around the eye-holes. Crystals then form around the bacterial populations and the biofilm starts to move down the lumenal surfaces of the catheters. The encrustation develops most extensively and generally blocks the catheter at or just below the eye-hole. There is a need to improve catheter design and manufacturing procedures for the eye-holes if the problems associated with the current devices are to be reduced.     

Bacterial adherence to bioinert and bioactive materials studied in vitro

In vitro, bioinert stainless steel and titanium alloy, and bioactive sintered hydroxyapatite and hydroxyapatite-coated titanium materials were exposed to Staphylococcus epidermidis to study bacterial adhesion. Scanning electron microscopy showed that fibrous strands interconnected the adherent bacteria, and that background matrix enclosed bacterial colonies. This adherent mode of growth may reduce the susceptibility of the bacteria to host clearance mechanisms and antibiotic therapy. Adherence assays revealed that bacterial adherence to sintered hydroxyapatite was higher than to the other 3 materials.     

In vitro and in vivo efficacy of a rifampin-loaded silicone catheter for the prevention of CSF shunt infections

Summary Infection of cerebrospinal fluid (CSF) shunts is one of the major complications associated with their use and is usually managed by shunt removal, temporary insertion of an external drainage and implantation of a new shunt system. We have evaluated the efficacy of a rifampin-loaded silicone ventricular catheter to prevent bacterial colonization and infection in vitro and in an animal model.On the basis of an incorporation process a rifampin-loaded catheter was developed which is capable of releasing rifampin in bacteriocidal concentrations for 60 days and more. In a stationary bacterial adherence assay usingS. epidermidis as test strain, the colonization resistance of the device was demonstrated.To assess the capability of the catheter to prevent CSF shunt infections, a rabbit model was developed which allowed the establishment of a reliable and reproducible CSF infection by implantation of silicone catheters into the ventricle and inoculatingS. epidermidis (minimal dose 10⁶ cfu) orS. aureus (minimal dose 10³ cfu). Rifampinloaded catheters (12 animals inoculated with S. epidermidis, 8 animals inoculated with S. aureus) were compared with non-loaded (14 animals inoculated with S. epidermidis, 19 animals inoculated with S. aureus) control catheters, and infection was documented by clinical, microbiological and histological methods.In contrast to the control group, none of the animals with rifampin-loaded catheters showed clinical signs of infection. Furthermore, in none of the materials obtained after sacrifice of the animals (catheter, brain tissue, CSF, blood) could the infecting bacteria be cultured, whereas in materials from animals with the unloaded catheter the infecting strains could always be cultured from the catheter and from surrounding brain tissue. The histological examination of catheter-adjacent tissue supported these findings.We conclude that a rifampin-loaded silicone ventricular catheter is capable of completely preventing bacterial colonization and infection by staphylococci as the main causative organisms in CSF shunt infections and should be further evaluated in clinical trials.