Direct confocal microscopy studies of the bacterial colonization in vitro of a silver-coated heart valve sewing cuff

Silver Diamine Fluoride as a Medicament for the Indirect Pulp Therapy in Primary Teeth: A Review of the Literature

Silver diamine fluoride (SDF) has been demonstrated to be effective in arresting caries lesions and, recently, clinical trials have assessed the effectiveness of SDF as a medicament for indirect pulp therapy (IPT) in primary teeth. This review aims to summarize the literature related to the use of SDF and find out if SDF can be used as an effective material for IPT. A literature search was undertaken on electronic databases including PubMed, MEDLINE, ScienceDirect, and Google Scholar, which elicited 50 studies employing different materials in the IPT of primary molars; however, of them, only four clinical trials used SDF as indirect pulp capping (IPC) material. SDF has the potential to be a useful material for IPT in primary teeth. It is a handy choice for pediatric dentists due to its minimum invasiveness, ease of application, and ability to stop the progression of caries. However, more studies are needed to determine whether SDF can be used routinely for IPT and whether it can even replace the currently available materials, as well as to fully realize its potential and establish criteria for its ideal application in IPT procedures.

Fungal-derived Selenium Nanoparticles and Their Potential Applications in Electroless Silver Coatings for Preventing Pin-tract Infections

Pin-tract infections (PTIs) are a common complication of external fixation of fractures and current strategies for preventing PTIs have proven to be ineffective. Recent advances show that the use of anti-infection coatings with local antibacterial activity may solve this problem. Selenium has been considered as a promising anti-infection agent owing to its antibacterial and antibiofilm activities. In this study, selenium nanoparticles (SeNPs) were synthesized via a cost-effective fungi-mediated biorecovery approach and demonstrated excellent stability and homogeneity. To investigate their anti-infection potential, the SeNPs were doped in silver coatings through an electroless plating process and the silver–selenium (Ag–Se) coatings were tested for antibacterial and antibiofilm properties against Staphylococcus aureus F1557 and Escherichia coli WT F1693 as well as corrosion resistance in simulated body fluid. It was found that the Ag–Se coating significantly inhibited S.aureus growth and biofilm formation on the surface, reducing 81.2% and 59.7% of viable bacterial adhesion when compared with Ag and Ag–PTFE-coated surfaces after 3 days. The Ag–Se coating also exhibited improved corrosion resistance compared with the Ag coating, leading to a controlled release of Ag⁺, which in turn reduced the risk of cytotoxicity against hFOBs. These results suggest that the fungal-derived SeNPs may have potential in use as implant coatings to prevent PTIs.

Comparative efficacy of linezolid and vancomycin for endotracheal tube MRSA biofilms from ICU patients

PURPOSE

To compare the efficacy of systemic treatment with linezolid (LNZ) versus vancomycin (VAN) on methicillin-resistant Staphylococcus aureus (MRSA) burden and eradication in endotracheal tube (ETT) biofilm and ETT cuff from orotracheally intubated patients with MRSA respiratory infection.

METHODS

Prospective observational clinical study was carried out at four European tertiary hospitals. Plasma and endotracheal aspirate (ETA) levels of LNZ and VAN were determined 72 h after treatment initiation through high-performance liquid chromatography or bioassay. LNZ or VAN concentration in the ETT biofilm and MRSA burden and eradication was determined upon extubation. The minimum inhibitory concentration (MIC) for LNZ and VAN was assessed by E-test strips (Biomerieux®). Scanning electron microscopy images were obtained, and ETT biofilm thickness was compared between groups.

RESULTS

Twenty-five patients, 15 treated with LNZ and 10 with VAN, were included in the study. LNZ presented a significantly higher concentration (μg/mL) than VAN in ETT biofilm (72.8 [1.3-127.1] vs 0.4 [0.4-1.3], p < 0.001), although both drugs achieved therapeutic plasma levels 72 h after treatment initiation. Systemic treatment with LNZ achieved lower ETT cuff MRSA burdens than systemic treatment with VAN. Indeed, LNZ increased the MRSA eradication rate in ETT cuff compared with VAN (LNZ 75%, VAN 20%, p = 0.031).

CONCLUSIONS

In ICU patients with MRSA respiratory infection intubated for long periods, systemic treatment with LNZ obtains a greater beneficial effect than VAN in limiting MRSA burden in ETT cuff.

Silver nanoparticle deposited implants to treat osteomyelitis

In this study, electrolytically deposited strongly adherent silver nanoparticles on stainless-steel (SS) implants were used for in situ osteomyelitis treatment. Samples were heat treated to enhance adhesion of silver on 316 L SS. Ex vivo studies were performed to measure silver-release profiles from the 316 L SS screws inserted in equine cadaver bones. No change in the release profiles of silver ions were observed in vitro between the implanted screws and the control. In vivo studies were performed using osteomyelitic rabbit model with 3 mm diameter silver-deposited 316 L SS pins at two different doses of silver: high and low. Infection control ability of the pins for treating osteomyelitis in a rabbit model was measured using bacteriologic, radiographic, histological, and scanning electron microscopic studies. Silver-coated pins, especially high dose, offered a promising result to treat infection in animal osteomyelitis model without any toxicity to major organs. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1073-1083, 2018.

Simple and Specific Grafting of Antibacterial Peptides on Silicone Catheters

To fight against nosocomial infection initiated by colonization of medical devices, a strategy enabling the direct and fast functionalization of silicone surfaces is proposed. This strategy proceeds in a site-specific way using original hybrid silylated antibacterial peptides. This safe and up-scalable method guarantees a covalent and robust immobilization with the correct orientation of the bioactive moiety. Importantly it also avoids multi-step chemical modifications of the surface or multi-layer polymer coatings. As proof of concept, antibacterial silicone catheter has been prepared whose immediate and long term efficiency is superior by comparison to similar silver-embedded materials.

Local Application of Probiotic Bacteria Prophylaxes against Sepsis and Death Resulting from Burn Wound Infection

Objective

To determine if local prophylactic application of probiotic bacteria to burn wounds will prevent death in a mouse model of burn wound sepsis.

Background

Infection remains the most common complication after burn injury and can result in sepsis and death, despite the use of topical and systemic antibiotics. Pseudomonas aeruginosa is a frequently implicated pathogen. Local application of probiotics directly to burn wounds is an attractive novel intervention that avoids the pitfalls of standard antibiotic therapies.

Methods

A burn-sepsis model was established using a sub-eschar injection of bioluminescent P. aeruginosa; infection was tracked using a charge-coupled camera. Full-thickness burn injuries were placed on the dorsums of adult mice; the injured sites were then treated with vehicle (burn wound control), probiotics (Lactobacillus plantarum only), pathogenic bacteria (Pseudomonas aeruginosa only), or probiotics plus pathogen (Lactobacillus plus Pseudomonas). Animals were monitored until death/moribundity or for one week, then sacrificed. Harvested tissues were subjected to imaging and molecular assays.

Results

Control and probiotic-only animals showed no mortality (100% survival) at one week. Pseudomonas-only animals showed > 90% mortality within 40 hours of infection. In contrast, animals treated with probiotics plus Pseudomonas showed less than 10% mortality. Use of bioluminescent Pseudomonas bacteria demonstrated that probiotic therapy inhibited septicemic accumulation of the pathogen in remote organs. In addition, probiotic therapy successfully suppressed the infection-dependent induction of TNF-α and interleukins 6 and 10 in the liver.

Conclusions

Local probiotic therapy shows great potential as a valuable adjunct in the management of complicated burn injury.

Toxicity mechanism of titanium dioxide and zinc oxide nanoparticles against food pathogens

Food preservation is an important field of research. It extends the shelf life of major food products. Our current study is based on food preservation through TiO₂ and ZnO nanoparticles. TiO₂ and ZnO are biocompatible nanomaterial. The biocompatibility of the materials were established through toxicity studies on cell lines. Titanium dioxide and Zinc Oxide nanoparticle were synthesized by wet chemical process. They are characterized by X-Ray diffraction and TEM. The antibacterial activities of both the materials were analysed to ensure their effectiveness as food preservative against Salmonella typhi, Klebsiella pneumoniae and Shigella flexneri. The results indicates that TiO₂ and ZnO nanoparticle inhibits Salmonella, Klebsiella and Shigella. The mode of action is by the generation of ROS in cases of Salmonella, Klebsiella. Mode of action in Shigella is still unclear. It was also proved that TiO₂ and ZnO nanoparticle are biocompatible materials.

Fewer Bacteria Adhere to Softer Hydrogels

Clinically, biofilm-associated infections commonly form on intravascular catheters and other hydrogel surfaces. The overuse of antibiotics to treat these infections has led to the spread of antibiotic resistance and underscores the importance of developing alternative strategies that delay the onset of biofilm formation. Previously, it has been reported that during surface contact, bacteria can detect surfaces through subtle changes in the function of their motors. However, how the stiffness of a polymer hydrogel influences the initial attachment of bacteria is unknown. Systematically, we investigated poly(ethylene glycol) dimethacrylate (PEGDMA) and agar hydrogels that were 20 times thicker than the cumulative size of bacterial cell appendages, as a function of Young's moduli. Soft (44.05-308.5 kPa), intermediate (1495-2877 kPa), and stiff (5152-6489 kPa) hydrogels were synthesized. Escherichia coli and Staphylococcus aureus attachment onto the hydrogels was analyzed using confocal microscopy after 2 and 24 h incubation periods. Independent of hydrogel chemistry and incubation time, E. coli and S. aureus attachment correlated positively to increasing hydrogel stiffness. For example, after a 24 h incubation period, there were 52 and 82% fewer E. coli adhered to soft PEGDMA hydrogels than to the intermediate and stiff PEGDMA hydrogels, respectively. A 62 and 79% reduction in the area coverage by the Gram-positive microbe S. aureus occurred after 24 h incubation on the soft versus intermediate and stiff PEGDMA hydrogels. We suggest that hydrogel stiffness is an easily tunable variable that could potentially be used synergistically with traditional antimicrobial strategies to reduce early bacterial adhesion and therefore the occurrence of biofilm-associated infections.

The effect of polyhexamethylene guanidine hydrochloride (PHMG) derivatives introduced into polylactide (PLA) on the activity of bacterial enzymes

The present study was aimed at investigating bactericidal properties of polylactide (PLA) films containing three different polyhexamethylene guanidine hydrochloride (PHMG) derivatives and effect of the derivatives on extracellular hydrolytic enzymes and intracellular dehydrogenases. All PHMG derivatives had a slightly stronger bactericidal effect on Staphylococcus aureus than on E. coli but only PHMG granular polyethylene wax (at the concentration of at least 0.6 %) has a bactericidal effect. PHMG derivatives introduced into PLA affected the activity of microbial hydrolases to a small extent. This means that the introduction of PHMG derivatives into PLA will not reduce its enzymatic biodegradation significantly. On the other hand, PHMG derivatives introduced into PLA strongly affected dehydrogenases activity in S. aureus than in E. coli.

Bacterial biofilms on implanted suture material are a cause of surgical site infection

BACKGROUND

Surgical site infection (SSI) has been estimated to occur in up to 5% of all procedures, accounting for up to 0.5% of all hospital costs. Bacterial biofilms residing on implanted foreign bodies have been implicated as contributing or causative factors in a wide variety of infectious scenarios, but little consideration has been given to the potential for implanted, submerged suture material to act as a host for biofilm and thus serve as a nidus of infection.

METHODS

We report a series of 15 patients who underwent open Roux-en-Y gastric bypass (with musculofascial closure with permanent, multifilament sutures) who developed longstanding and refractory SSIs in the abdominal wall. Explanted suture material at subsequent exploration was examined for biofilm with confocal laser-scanning microscopy (CLSM) and fluorescence in situ hybridization (FISH).

RESULTS

All 15 patients at re-exploration were found to have gross evidence of a "slimy" matrix or dense reactive granulation tissue localized to the implanted sutures. Confocal laser-scanning microscopy revealed abundant biofilm present on all sutures examined; FISH was able to identify the presence of specific pathogens in the biofilm. Complete removal of the foreign bodies (and attendant biofilms) resulted in all cases in cure of the SSI.

CONCLUSION

Bacterial biofilms on implanted suture material can manifest as persistent surgical site infections that require complete removal of the underlying foreign body substrata for resolution.

Bacteria-material surface interactions: methodological development for the assessment of implant surface induced antibacterial effects

The choice of material for implanted prostheses is of great importance concerning bacterial colonization and biofilm formation. Consequently, methods to investigate bacterial behavior are needed in order to develop new infection resistant surfaces. In this study, different methodological setups were used to evaluate the antimicrobial effect of photocatalytic titanium oxide and silver surfaces. Biofilm formation and eradication under static and dynamic culture conditions were studied with the use of the following analytical techniques: viable colony-forming unit (CFU) counting, imprinting, fluorescence, and bioluminescence. The present study demonstrates that different methods are needed in order to evaluate the prophylactic and treatment effects on planktonic and biofilm bacteria and to assess the antimicrobial effect of different surface treatments/coatings. Choosing the right antibacterial testing model for the specific application is also of great importance. Both in situ approaches and indirect methods provide valuable complementary information.

A Novel Qualitative and Quantitative Biofilm Assay Based on 3D Soft Tissue

The lack of predictable in vitro methods to analyze antimicrobial activity could play a role in the development of resistance to antibiotics. Current used methods analyze planktonic cells but for the method to be clinically relevant, biofilm in in vivo like conditions ought to be studied. Hence, our group has developed a qualitative and quantitative method with in vivo like 3D tissue for prediction of antimicrobial activity in reality. Devices (wound dressings) were applied on top of Pseudomonas aeruginosa inoculated Muller-Hinton (MH) agar or 3D synthetic soft tissues (SST) and incubated for 24 hours. The antibacterial activity was then analyzed visually and by viable counts. On MH agar two out of three silver containing devices showed zone of inhibitions (ZOI) and on SST, ZOI were detected for all three. Corroborating results were found upon evaluating the bacterial load in SST and shown to be silver concentration dependent. In conclusion, a novel method was developed combining visual rapid screening and quantitative evaluation of the antimicrobial activity in both tissue and devices. It uses tissue allowing biofilm formation thus mimicking reality closely. These conditions are essential in order to predict antimicrobial activity of medical devices in the task to prevent device related infections.

A simple method for quantifying biomass cell and polymer distribution in biofilms

Biofilms are ubiquitous and play an essential role in both environmental processes and hospital infections. Standard methods are not capable of quantifying biomass concentration in dilute suspensions. Furthermore, standard techniques cannot differentiate biomass composition. In this study, a user-friendly technique was developed for measuring biomass cell and polymer content in detached biofilms using a standard coulter counter. The method was demonstrated for an environmentally relevant strain of Pseudomonas aeruginosa (Schroeter) Migula grown in a bioreactor and also for a medically relevant strain of P. aeruginosa (PAO1) grown on standard growth pegs. Results were compared and validated by standard assays, including EPA method 1684 for measuring biomass, microscopic direct counts, and a crystal violet staining assay. The minimum detection limit for the coulter counter method (0.07 mg-biomass L(-1)) was significantly lower than the EPA method 1684 (1.9 ± 0.4 mg/L) and the crystal violet assay (1.1 ± 0.2 mg L(-1)). However, the coulter counter method is limited to dilute biomass samples (below 204 ± 16 mg L(-1)) due to clogging of the aperture tube. While biomass measurements are useful, the major advantage of the coulter counter method is the ability to directly determine EPS, cell, and aggregate fractions after mild chemical treatment. The rapid technique (4-5 min per sample) was used to measure biomass fractions in dispersed P. aeruginosa (Schroeter) and PAO1 biofilms. This technique will be critical for understanding biofilm formation/dispersal.

Can a novel silver nano coating reduce infections and maintain cell viability in vitro?

Herein we report a facile layer-by-layer method for creating an antimicrobial coating composed of silver nanoparticles on medical grade titanium test discs. Nanoscale silver nanoparticle layers are attached to the titanium orthopedic implant material via aminopropyltriethoxy silane crosslinker that reacts with neighboring silane moieties to create an interconnected network. A monolayer of silane, followed by a monolayer of silver nanoparticles would form one self-assembled layer and this process can be repeated serially, resulting in increased silver nanoparticles deposition. The release rate of silver ion increases predictably with increasing numbers of layers and at appropriate thicknesses these coatings demonstrate 3-4 log reduction of viable Escherichia coli and Staphylococcus aureus bacteria. Increasing the thickness of the coatings resulted in reduced bacterial colonization as determined by fluorescent staining and image analysis. Interestingly, the cytotoxicity of murine 3T3 cells as quantified by fluorescent staining and flow cytometry, was minimal and did not vary significantly with the coating thickness. Additionally, these coatings are mechanically stable and resist delamination by orthogonal stress test. This simple layer-by-layer coating technique may provide a cost-effective and biocompatible method for reducing microbial colonization of implantable orthopedic devices.

Infection of orthopedic implants with emphasis on bacterial adhesion process and techniques used in studying bacterial-material interactions

Staphylococcus comprises up to two-thirds of all pathogens in orthopedic implant infections and they are the principal causative agents of two major types of infection affecting bone: septic arthritis and osteomyelitis, which involve the inflammatory destruction of joint and bone. Bacterial adhesion is the first and most important step in implant infection. It is a complex process influenced by environmental factors, bacterial properties, material surface properties and by the presence of serum or tissue proteins. Properties of the substrate, such as chemical composition of the material, surface charge, hydrophobicity, surface roughness and the presence of specific proteins at the surface, are all thought to be important in the initial cell attachment process. The biofilm mode of growth of infecting bacteria on an implant surface protects the organisms from the host immune system and antibiotic therapy. The research for novel therapeutic strategies is incited by the emergence of antibiotic-resistant bacteria. This work will provide an overview of the mechanisms and factors involved in bacterial adhesion, the techniques that are currently being used studying bacterial-material interactions as well as provide insight into future directions in the field.

Does elevating silver content in zinc-based glass polyalkenoate cements increase their antibacterial efficacy against two common bacteria using the agar gel diffusion method?

The authors have previously shown that it is possible to incorporate silver into a soda-zinc-silicate glass and subsequently form a glass polyalkenoate cement from it. The objective of the research described herein is to determine if incremental increases in the silver content of these glass polyalkenoate cements will increase their antibacterial efficacy against gram-positive and gram-negative bacteria using the accepted spread plate method. Four glass polyalkenoate cements were formulated; three contained increasing amounts of silver incorporated into them (cements A, B, and C, containing 0.33 mol%, 0.66 mol%, and 0.99 mol% silver, respectively) and a fourth contained no silver, which acted as a control (control cement). The handling properties of the glass polyalkenoate cements were evaluated, where working times were around 2 min and setting times ranged from 1 h 17 min to 2 h 41 min. Inductively coupled plasma atomic emission spectroscopy was employed to determine silver ion release with cement maturation for up to 14 days. The majority of silver ions were released within the first 24 h, with up to 2 mg/L cumulative ion release recorded up to 14 days. The antibacterial properties of the coatings were evaluated against Staphylococcus aureus and Pseudomonas aeruginosa bacteria. The silver-glass polyalkenoate cements exhibited antibacterial effect against both bacterial strains. The maximum inhibition zones recorded against S. aureus was 14.8 mm (SD ± 1.11) and against P. aeruginosa was 20.6 mm (SD ± 0.81). Cement B had a greater antibacterial effect compared to cement A, however, cements B and C had comparable antibacterial effects after 14 days even though cement C contained 0.33 mol% more silver than B. This indicates that by increasing the silver content in these cements, the antibacterial efficacy increases to a point, but there is a threshold where further silver ion release does not increase the antibacterial effect.

Hard implant coatings with antimicrobial properties

Infection of orthopaedic implants often leads to inflammation immediately after surgery and increases patient morbidity due to repetitive operations. Silver ions have been shown to combine good biocompatibility with a low risk of inducing bacterial resistance. In this study a physical vapour deposition system using both arc deposition and magnetron sputtering has been utilized to produce silver ion doped TiN coatings on Ti substrates. This biphasic system combines the advantages of silver induced bactericidity with the good mechanical properties of TiN. Crystallographic analysis by X-ray diffraction showed that silver was deposited as well in its elementary form as it was incorporated into the crystal lattice of TiN, which resulted in increasing hardness of the TiN-coatings. Elution experiments revealed a continuous release of Ag ions in phosphate buffered saline. The coatings showed significant inhibitory effects on the growth of Staphylococcus epidermidis and Staphylococcus aureus and practically no cell-toxicity in cytocompatibility tests.

Silver-doped calcium phosphate cements with antimicrobial activity

There is a current need for the localised delivery of antibiotics in order to treat implant-based bacterial infections. Existing treatments use non-resorbable materials such as poly(methyl methacrylate) beads loaded with antibiotics; unfortunately, as they are not resorbable, these beads require secondary surgery for removal. Calcium phosphate cements have considerable potential for the localised delivery of drugs since they can be resorbed to some extent within the body, eliminating the need for a secondary surgical procedure. Therefore, in this study, the efficacy of both hydroxyapatite and brushite cements in the delivery of silver ions has been investigated. The activity of the Ag(+) released from the cements was assessed against the growth of both Staphylococcus aureus and Staphylococcus epidermidis; the brushite cement exhibited excellent antibacterial properties and also showed an increase in compressive strength of over 30%. In this study we have found that with a few changes in Ag(+) concentration it should be possible to produce a fully resorbable bone replacement material that is combined with an antibacterial scaffold with controlled release over a period of time, which is likely to inhibit bacterial infections associated with implantation procedures.

Vascular prostheses with covalently bound gentamicin and amikacin reveal superior antibacterial properties than silver-impregnated ones--an in vitro study

OBJECTIVE

This study aims to compare the antibacterial activities of vascular prostheses: silver-impregnated and modified with covalently immobilised antibiotics.

MATERIALS AND METHODS

Six types of protein-sealed vascular prostheses were modified with amikacin and gentamicin according to the method described in the Polish Patent Office. Their antimicrobial properties were estimated against 14 reference and clinical strains and compared with those of InterGard Silver grafts. Cytotoxicity of the tested grafts was estimated against human skin fibroblasts.

RESULTS

Prostheses modified with antibiotics in a stable covalent mode were found to be much more effective against bacterial growth and biofilm formation, as well as in case of methicillin-resistant Staphylococcus aureus (MRSA), than InterGard Silver. They inhibited the bacterial growth for at least 30 days, without losing higher than 10% of the initial amount of its drug content. They were also good, non-toxic matrices for growth of human skin fibroblasts.

CONCLUSIONS

Prostheses modified with covalently immobilised antibiotic according to our technique are much more effective than InterGard Silver at protection against bacterial growth. They are also compatible with human skin fibroblasts.

Antibacterial coatings for medical devices based on glass polyalkenoate cement chemistry

A biofilm is an accumulation of micro-organisms and their extracellular products forming a structured community on a surface. Biofilm formation on medical devices has severe health consequences as bacteria growing in this lifestyle are tolerant to both host defense mechanisms and antibiotic therapies. However, silver and zinc ions inhibit the attachment and proliferation of immature biofilms. The objective of this study is to evaluate whether it is possible to produce silver and zinc-containing glass polyalkenoate cement (GPC) coatings for medical devices that have antibacterial activity and which may therefore inhibit biofilm formation on a material surface. Two silver and zinc-containing GPC coatings (A and B) were synthesised and coated onto Ti6Al4V discs. Their handling properties were characterised and atomic absorption spectrometery was employed to determine zinc and silver ion release with coating maturation up to 30 days. The antibacterial properties of the coatings were also evaluated against Staphylococcus aureus and a clinical isolate of Pseudomonas aeruginosa using an agar diffusion assay method. The majority of the zinc and silver ions were released within the first 24 h; both coatings exhibited antibacterial effect against the two bacterial strains, but the effect was more intense for B which contained more silver and less zinc than A. Both coatings produced clear zones of inhibition with each of the two organisms tested. In this assay, Ps. aeruginosa was more sensitive than S. aureus. The diameters of these zones were reduced after the coating had been immersed in water for varying periods due to the resultant effect on ion release.

Pathologic Analysis of 19 Heart Valves With Silver-Coated Sewing Rings

OBJECTIVE

The St. Jude Medical Silzone (Silzone) mechanical heart valve was voluntarily recalled (January 2000) due to an unusually high incidence of paravalvular leaks. We present the first series of human morphological data on the failure of these valves.

METHODS

Nineteen Silzone valves were evaluated from the 176 Silzone valves implanted in 147 patients at our institution between 1997 and 1999. Explanted prostheses were fixed in 10% formalin, photographed, and X-rayed. Histological sections were collected from the sewing cuff, accompanying tissues, and thrombus. For comparison, six age-matched SJM-standard valves were similarly analyzed.

RESULTS

Nineteen Silzone valves from 16 patients (10 male, six female, 52.0 +/- 15.2 years) were examined. Significantly more mitral (15/95) prostheses were removed than aortic (4/81) despite the nearly equal number implanted (p = 0.027). Fifteen of the Silzone valves (13/16 patients) were explanted in the early postoperative period (within six months of implantation), although collection continued for eight years after our institution stopped implanting them. The common indications for surgical explantation were paravalvular leak (8/12) and clinically suspected infective endocarditis (IE) (four patients, five valves). IE was not confirmed by histology or culture in any valve. The sewing cuffs of many Silzone valves showed large regions of pannus, granulation tissue, and purulent exudate. Polymorphonuclear leukocytes were more common in the sewing cuff of Silzone valves; however, the cellular infiltrate was superficial when compared to SJM-standard valves.

CONCLUSION

This is the largest morphologically analyzed series of Silzone explants. It demonstrates a consistent pattern of atypical tissue incorporation into the silver-coated sewing ring particularly in the mitral position. Clinical and morphologic features of IE (sterile) are seen in the early postimplant period. Prosthesis-related problems were almost wholly seen at the mitral site, in our group. Our current data indicate that although early failure due to dehiscence and paravalvular leak is a problem, Silzone valves that "survive" past six months will likely function as well as the SJM-standard prosthesis.

Antimicrobial titanium/silver PVD coatings on titanium

BACKGROUND

Biofilm formation and deep infection of endoprostheses is a recurrent complication in implant surgery. Post-operative infections may be overcome by adjusting antimicrobial properties of the implant surface prior to implantation. In this work we described the development of an antimicrobial titanium/silver hard coating via the physical vapor deposition (PVD) process.

METHODS

Coatings with a thickness of approximately 2 mum were deposited on titanium surfaces by simultaneous vaporisation of both metals in an inert argon atmosphere with a silver content of approximately 0.7-9% as indicated by energy dispersive X-ray analysis. On these surfaces microorganisms and eukaryotic culture cells were grown.

RESULTS

The coatings released sufficient silver ions (0.5-2.3 ppb) when immersed in PBS and showed significant antimicrobial potency against Staphylococcus epidermis and Klebsiella pneumoniae strains. At the same time, no cytotoxic effects of the coatings on osteoblast and epithelial cells were found.

CONCLUSION

Due to similar mechanical performance when compared to pure titanium, the TiAg coatings should be suitable to provide antimicrobial activity on load-bearing implant surfaces.

Biofilm theory can guide the treatment of device-related orthopaedic infections

Direct observations of the surfaces of orthopaedic prostheses that have failed and of bone affected by osteomyelitis with and without the presence of a prosthesis have shown that the bacteria that cause these infections live in well-developed biofilms. The cells within these matrix-enclosed surface-associated communities are protected from host defenses and antibiotics, and clinical experience has shown that they must be removed physically before the infection can be resolved. The biofilm etiology of these diseases demands new diagnostic methods because biofilm cells typically do not grow on agar plates when recovered by scraping or swabbing. I will recommend new molecular and immunologic diagnostic methods that have been useful in other biofilm infections. These diseases progress through quiescent periods that alternate with acute exacerbations, and clinicians must realize that antibiotic therapy can control the acute phases but cannot resolve the basic biofilm nidus of the infection. Now that it has been realized that these orthopaedic infections are caused by relatively common biofilm-forming bacterial pathogens, new technologies that deliver very high concentrations of antibiotics locally and "on demand" and novel molecular "mimics" that block the signals that control biofilm formation need to be examined.

Role of biofilms in neurosurgical device-related infections

Bacterial biofilms have recently been shown to be important in neurosurgical device-related infections. Because the concept of biofilms is novel to most practitioners, it is important to understand that both traditional pharmaceutical therapies and host defense mechanisms that are aimed at treating or overcoming free-swimming bacteria are largely ineffective against the sessile bacteria in a biofilm. Bacterial biofilms are complex surface-attached structures that are composed of an extruded extracellular matrix in which the individual bacteria are embedded. Superimposed on this physical architecture is a complex system of intercellular signaling, termed quorum sensing. These complex organizational features endow biofilms with numerous microenvironments and a concomitant number of distinct bacterial phenotypes. Each of the bacterial phenotypes within the biofilm displays a unique gene expression pattern tied to nutrient availability and waste transport. Such diversity provides the biofilm as a whole with an enormous survival advantage when compared to the individual component bacterial cells. Thus, it is appropriate to view the biofilm as a multicellular organism, akin to metazoan eukaryotic life. Bacterial biofilms are much hardier than free floating or planktonic bacteria and are primarily responsible for device-related infections. Now that basic research has demonstrated that the vast majority of bacteria exist in biofilms, the paradigm of biofilm-associated chronic infections is spreading to the clinical world. Understanding how these biofilm infections affect patients with neurosurgical devices is a prerequisite to developing strategies for their treatment and prevention.

A microbiological and confocal microscopy study documenting a slime-producing Staphylococcus epidermidis isolated from a nylon corneal suture of a patient with antibiotic-resistant endophthalmitis

BACKGROUND

We describe a case of posttraumatic endophthalmitis unresponsive to systemic (amoxicillin+clavulanic acid and piperacillin/tazobactam), intra-ocular (vancomycin) and topical (ofloxacin, tetracycline and sulfametoxazole) antibiotic therapy. Microbiological and confocal microscopy studies of a nylon corneal suture revealed the presence of a slime-producing strain of Staphylococcus epidermidis.

METHODS

We describe the history and clinical presentation of a 77-year-old man in whom a high-grade posttraumatic endophthalmitis resolved only after the removal of a single nylon corneal suture. Microbiological investigations of the aqueous, vitreous and suture were performed, and the propensity of the suture-associated isolate to form biofilm was assessed using confocal microscopy.

RESULTS

A single stain of S. epidermidis was isolated from both aqueous and vitreous specimens and from the suture. The planktonic form of the isolate was susceptible in vitro to the antibiotics administered to the patient, but the strain was capable of forming biofilms and this phenotype showed resistance to high concentrations of the same antibiotics.

CONCLUSIONS

The presence of a slime-producing strain of S. epidermidis should be considered in endophthalmitis that is unresponsive to specific antibiotic therapy, especially in cases in which an intra-ocular foreign body (e.g., a suture) is present.

Use of an oxonol dye in combination with confocal laser scanning microscopy to monitor damage to Staphylococcus aureus cells during colonisation of silver-coated vascular grafts

The antimicrobial silver-coating of medical prostheses is regarded as a means to reduce the risk of bacterial colonisation after implantation. The effect of a silver-coating of vascular grafts on biofilm formation was assessed in batch cultures of Staphylococcus aureus, using confocal laser scanning microscopy. Total cells in biofilms were analysed by staining with the DNA-binding fluorochrome SYTO 62 and the proportion of damaged cells was quantified with the membrane potential-sensitive dye bis-(1,3-dibutylbarbituric acid) trimethine oxonol. Both the extent of biofilm formation and the proportion of viable biofilm cells were significantly diminished on the surface of the silver-coated vascular grafts compared with uncoated controls, probably due to the antimicrobial activity of silver ions released from the silver-coated graft surface.

In vitro and ex vivo activities of minocycline and EDTA against microorganisms embedded in biofilm on catheter surfaces

Minocycline-EDTA (M-EDTA) flush solution has been shown to prevent catheter-related infection and colonization in a rabbit model and in hemodialysis patients. We undertook this study in order to determine the activities of M-EDTA against organisms embedded in fresh biofilm (in vitro) and mature biofilm (ex vivo). For the experiment with the in vitro model, a modified Robbin's device (MRD) was used whereby 25 catheter segments were flushed for 18 h with 10(6) CFU of biofilm-producing Staphylococcus epidermidis, Staphylococcus aureus, and Candida albicans per ml. Subsequently, each of the catheter segments was incubated in one of the following solutions: (i) streptokinase, (ii) heparin, (iii) broth alone, (iv) vancomycin, (v) vancomycin-heparin, (vi) EDTA, (vii) minocycline (high-dose alternating with low-dose), or (viii) M-EDTA (low-dose minocycline alternating with high-dose minocycline were used to study the additive and synergistic activities of M-EDTA). All segments were cultured quantitatively by scrape sonication. For the experiment with the ex vivo model, 54 catheter tip segments removed from patients and colonized with bacterial organisms by roll plate were longitudinally cut into two equal segments and exposed to either saline, heparin, EDTA, or M-EDTA (with high-dose minocycline). Subsequently, all segments were examined by confocal laser electron microscopy. In the in vitro MRD model, M-EDTA (with a low concentration of minocycline) was significantly more effective than any other agent in reducing colonization of S. epidermidis, S. aureus, and C. albicans (P < 0.01). M-EDTA (with a high concentration of minocycline) eradicated all staphylococcal and C. albicans organisms embedded in the biofilm. In the ex vivo model, M-EDTA (with a high concentration of minocycline) reduced bacterial colonization more frequently than EDTA or heparin (P < 0.01). We concluded that M-EDTA is highly active in eradicating microorganisms embedded in fresh and mature biofilm adhering to catheter surfaces.

The evolution of bioprosthetic heart valve design and its impact on durability

Bioprosthetic heart valves have evolved over the years into remarkably useful and predictable devices. During this process, a number of specific designs have come and gone, and a few have remained. Many design changes were successful, and many were not. This article will describe the successes and failures of the various bioprosthetic valve designs and will detail the specific reasons why a particular design change succeeded or failed to improve bioprosthetic valve performance.

Biological efficacy of electroless-deposited silver on plasma activated polyurethane

Silver coating of catheters has been shown to have inhibitory effects on bacterial growth and adhesion to catheter surfaces. In this study, plasma-modification was used to enhance the adhesion of an electroless silver coating on polyurethane. Both the antibacterial and antiadhesive properties of these coatings were investigated. Bacterial growth was inhibited in cultures exposed to silver-treated polyurethane compared to unmodified polyurethane. Higher growth inhibition was observed for polyurethane surfaces with lower silver coverage. Bacterial adhesion was completely inhibited on all silver-coated surfaces.

Bacterial silver resistance: molecular biology and uses and misuses of silver compounds

Resistance to silver compounds as determined by bacterial plasmids and genes has been defined by molecular genetics. Silver resistance conferred by the Salmonella plasmid pMGH100 involves nine genes in three transcription units. A sensor/responder (SilRS) two-component transcriptional regulatory system governs synthesis of a periplasmic Ag(I)-binding protein (SilE) and two efflux pumps (a P-type ATPase (SilP) plus a three-protein chemiosmotic RND Ag(I)/H+ exchange system (SilCBA)). The same genes were identified on five of 19 additional IncH incompatibility class plasmids but thus far not on other plasmids. Of 70 random enteric isolates from a local hospital, isolates from catheters and other Ag-exposed sites, and total genomes of enteric bacteria, 10 have recognizable sil genes. The centrally located six genes are found and functional in the chromosome of Escherichia coli K-12, and also occur on the genome of E. coli O157:H7. The use of molecular epidemiological tools will establish the range and diversity of such resistance systems in clinical and non-clinical sources. Silver compounds are used widely as effective antimicrobial agents to combat pathogens (bacteria, viruses and eukaryotic microorganisms) in the clinic and for public health hygiene. Silver cations (Ag+) are microcidal at low concentrations and used to treat burns, wounds and ulcers. Ag is used to coat catheters to retard microbial biofilm development. Ag is used in hygiene products including face creams, "alternative medicine" health supplements, supermarket products for washing vegetables, and water filtration cartridges. Ag is generally without adverse effects for humans, and argyria (irreversible discoloration of the skin resulting from subepithelial silver deposits) is rare and mostly of cosmetic concern.

Interactions between biocide cationic agents and bacterial biofilms

The resistance of bacterial biofilms to physical and chemical agents is attributed in the literature to various interconnected processes. The limitation of mass transfer alters the growth rate, and physiological changes in the bacteria in the film also appear. The present work describes an approach to determination of the mechanisms involved in the resistance of bacteria to quaternary ammonium compounds (benzalkonium chloride) according to the C-chain lengths of those compounds. For Pseudomonas aeruginosa CIP A 22, the level of resistance of the bacteria in the biofilm relative to that of planktonic bacteria increased with the C-chain length. For cells within the biofilm, the exopolysaccharide induced a characteristic increase in surface hydrophilicity. However, this hydrophilicity was eliminated by simple resuspension and washing. The sensitivity to quaternary ammonium compounds was restored to over 90%. Staphylococcus aureus CIP 53 154 had a very high level of resistance when it was in the biofilm form. A characteristic of bacteria from the biofilm was a reduction in the percent hydrophobicity, but the essential point is that this hydrophobicity was retained after the biofilm bacteria were resuspended and washed. The recovery of sensitivity was thus only partial. These results indicate that the factors involved in biofilm resistance to quaternary ammonium compounds vary according to the bacterial modifications induced by the formation of a biofilm. In the case of P. aeruginosa, we have underlined the involvement of the exopolysaccharide and particularly the three-dimensional structure (water channels). In the case of S. aureus, the role of the three-dimensional structure is limited and drastic physiological changes in the biofilm cells are more highly implicated in resistance.

Biofilms: survival mechanisms of clinically relevant microorganisms

Though biofilms were first described by Antonie van Leeuwenhoek, the theory describing the biofilm process was not developed until 1978. We now understand that biofilms are universal, occurring in aquatic and industrial water systems as well as a large number of environments and medical devices relevant for public health. Using tools such as the scanning electron microscope and, more recently, the confocal laser scanning microscope, biofilm researchers now understand that biofilms are not unstructured, homogeneous deposits of cells and accumulated slime, but complex communities of surface-associated cells enclosed in a polymer matrix containing open water channels. Further studies have shown that the biofilm phenotype can be described in terms of the genes expressed by biofilm-associated cells. Microorganisms growing in a biofilm are highly resistant to antimicrobial agents by one or more mechanisms. Biofilm-associated microorganisms have been shown to be associated with several human diseases, such as native valve endocarditis and cystic fibrosis, and to colonize a wide variety of medical devices. Though epidemiologic evidence points to biofilms as a source of several infectious diseases, the exact mechanisms by which biofilm-associated microorganisms elicit disease are poorly understood. Detachment of cells or cell aggregates, production of endotoxin, increased resistance to the host immune system, and provision of a niche for the generation of resistant organisms are all biofilm processes which could initiate the disease process. Effective strategies to prevent or control biofilms on medical devices must take into consideration the unique and tenacious nature of biofilms. Current intervention strategies are designed to prevent initial device colonization, minimize microbial cell attachment to the device, penetrate the biofilm matrix and kill the associated cells, or remove the device from the patient. In the future, treatments may be based on inhibition of genes involved in cell attachment and biofilm formation.

Influence of surface modifications to titanium on antibacterial activity in vitro

The antibacterial effect of surface modifications to titanium on Porphyromonas gingivalis ATCC 33277 and Actinobacillus actinomycetemcomitans ATCC 43718 was evaluated. Surface modifications were performed with dry processes including ion implantation (Ca+, N+, F+), oxidation (anode oxidation, titania spraying), ion plating (TiN, alumina), and ion beam mixing (Ag, Sn, Zn, Pt) with Ar+ on polished pure titanium plates. F+-implanted specimens significantly inhibited the growth of both P. gingivalis and A. actinomycetemcomitans than the polished titanium. The other surface-modified specimens did not exhibit effective antibacterial activity against both bacteria. No release of the fluorine ion was detected from F-implanted specimens under dissolution testing. This result and the characterization of the F+-implanted surfaces suggested that the possible antibacterial mechanism of the F+-implanted specimen was caused by the formation of a metal fluoride complex on the surfaces. In addition, F+-implanted surfaces did not inhibit the proliferation of fibroblast L929-cells. These findings indicate that surface modification by means of a dry process is useful in providing antibacterial activity of oral bacteria to titanium implants exposed to the oral cavity.