Silver-coated endotracheal tubes for prevention of ventilator-associated pneumonia in critically ill patients.

BACKGROUND: Ventilator-associated pneumonia (VAP) is one of the most common nosocomial infections in intubated and mechanically ventilated patients. Endotracheal tubes (ETTs) appear to be an independent risk factor for VAP. Silver-coated ETTs slowly release silver cations. It is these silver ions that appear to have a strong antimicrobial effect. Because of this antimicrobial effect of silver, silver-coated ETTs could be an effective intervention to prevent VAP in people who require mechanical ventilation for 24 hours or longer. OBJECTIVES: Our primary objective was to investigate whether silver-coated ETTs are effective in reducing the risk of VAP and hospital mortality in comparison with standard non-coated ETTs in people who require mechanical ventilation for 24 hours or longer. Our secondary objective was to ascertain whether silver-coated ETTs are effective in reducing the following clinical outcomes: device-related adverse events, duration of intubation, length of hospital and intensive care unit (ICU) stay, costs, and time to VAP onset. SEARCH METHODS: We searched the Cochrane Central Register of Controlled Trials (CENTRAL; 2014 Issue 10, MEDLINE, EMBASE, EBSCO CINAHL, and reference lists of trials. We contacted corresponding authors for additional information and unpublished studies. We did not impose any restrictions on the basis of date of publication or language. The date of the last search was October 2014. SELECTION CRITERIA: We included all randomized controlled trials (RCTs) and quasi-randomized trials that evaluated the effects of silver-coated ETTs or a combination of silver with any antimicrobial-coated ETTs with standard non-coated ETTs or with other antimicrobial-coated ETTs in critically ill people who required mechanical ventilation for 24 hours or longer. We also included studies that evaluated the cost-effectiveness of silver-coated ETTs or a combination of silver with any antimicrobial-coated ETTs. DATA COLLECTION AND ANALYSIS: Two review authors (GT, HV) independently extracted the data and summarized study details from all included studies using the specially designed data extraction form. We used standard methodological procedures expected by The Cochrane Collaboration. We performed meta-analysis for outcomes when possible. MAIN RESULTS: We found three eligible randomized controlled trials, with a total of 2081 participants. One of the three included studies did not mention the amount of participants and presented no outcome data. The 'Risk of bias' assessment indicated that there was a high risk of detection bias owing to lack of blinding of outcomes assessors, but we assessed all other domains to be at low risk of bias. Trial design and conduct were generally adequate, with the most common areas of weakness in blinding. The majority of participants were included in centres across North America. The mean age of participants ranged from 61 to 64 years, and the mean duration of intubation was between 3.2 and 7.7 days. One trial comparing silver-coated ETTs versus non-coated ETTs showed a statistically significant decrease in VAP in favour of the silver-coated ETT (1 RCT, 1509 participants; 4.8% versus 7.5%, risk ratio (RR) 0.64, 95% confidence interval (CI) 0.43 to 0.96; number needed to treat for an additional beneficial outcome (NNTB) = 37; low-quality evidence). The risk of VAP within 10 days of intubation was significantly lower with the silver-coated ETTs compared with non-coated ETTs (1 RCT, 1509 participants; 3.5% versus 6.7%, RR 0.51, 95% CI 0.31 to 0.82; NNTB = 32; low-quality evidence). Silver-coated ETT was associated with delayed time to VAP occurrence compared with non-coated ETT (1 RCT, 1509 participants; hazard ratio 0.55, 95% CI 0.37 to 0.84). The confidence intervals for the results of the following outcomes did not exclude potentially important differences with either treatment. There were no statistically significant differences between groups in hospital mortality (1 RCT, 1509 participants; 30.4% versus 26.6%, RR 1.09, 95% CI 0.93 to 1.29; low-quality evidence); device-related adverse events (2 RCTs, 2081 participants; RR 0.65, 95% CI 0.37 to 1.16; low-quality evidence); duration of intubation; and length of hospital and ICU stay. We found no clinical studies evaluating the cost-effectiveness of silver-coated ETTs. AUTHORS' CONCLUSIONS: This review provides limited evidence that silver-coated ETT reduces the risk of VAP, especially during the first 10 days of mechanical ventilation.

Bacterial infection as a likely cause of adverse reactions to polyacrylamide hydrogel fillers in cosmetic surgery.

BACKGROUND: The etiology of long-lasting adverse reactions to gel fillers used in cosmetic surgery is not known. Bacterial infection and immunological reaction to the product have been suggested. METHODS: We performed a case-control study, with 77 biopsies and 30 cytology specimens originating from 59 patients with adverse reactions to polyacrylamide gel, and 54 biopsies and 2 cytology specimens from 28 control subjects with no adverse reactions. Samples from 5 patients and 4 controls could not be investigated for presence of bacteria owing to limited material. Samples from the remaining 54 patients and 24 controls were systematically examined for the presence of bacteria by culture, 16S rRNA gene sequencing, Gram stain, and fluorescence in situ hybridization. RESULTS: Bacteria, mostly normal skin bacteria such as Staphylococcus epidermidis and Propionibacterium acnes, were identified in bacteriologically investigated samples from 53 of 54 patients (98%), and in none of the 24 controls (0%). The bacteria were lying in small clusters, which in symptomatic lesions were detected up to 5 years postinjection. CONCLUSIONS: Commensal bacteria of low virulence are capable of producing long-term infection in the presence of polyacrylamide filler in cosmetic surgery, possibly due to a biofilm mode of growth. Adequate skin preparation and use of sterile technique in these procedures are mandatory, but antibiotic prophylaxis prior to injection of nondegradable gels like polyacrylamide should be explored as well.

A Niclosamide-releasing hot-melt extruded catheter prevents Staphylococcus aureus experimental biomaterial-associated infection.

Biomaterial-associated infections are a major healthcare challenge as they are responsible for high disease burden in critically ill patients. In this study, we have developed drug-eluting antibacterial catheters to prevent catheter-related infections. Niclosamide (NIC), originally an antiparasitic drug, was incorporated into the polymeric matrix of thermoplastic polyurethane (TPU) via solvent casting, and catheters were fabricated using hot-melt extrusion technology. The mechanical and physicochemical properties of TPU polymers loaded with NIC were studied. NIC was released in a sustained manner from the catheters and exhibited in vitro antibacterial activity against Staphylococcus aureus and Staphylococcus epidermidis. Moreover, the antibacterial efficacy of NIC-loaded catheters was validated in an in vivo biomaterial-associated infection model using a methicillin-susceptible and methicillin-resistant strain of S. aureus. The released NIC from the produced catheters reduced bacterial colonization of the catheter as well as of the surrounding tissue. In summary, the NIC-releasing hot-melt extruded catheters prevented implant colonization and reduced the bacterial colonization of peri-catheter tissue by methicillin sensitive as well as resistant S. aureus in a biomaterial-associated infection mouse model and has good prospects for preclinical development.

In Vitro Bacterial Adhesion and Biofilm Formation on Fully Absorbable Poly-4-hydroxybutyrate and Nonabsorbable Polypropylene Pelvic Floor Implants.

Knitted polypropylene (PP) implants for the correction of pelvic organ prolapse have been associated with complications such as vaginal exposure, infection, and pain. Since certain complications may be linked to bacterial contamination and persistent inflammation, there is a rationale to develop a biocompatible implant that is less prone to bacterial adhesion and biofilm formation. Delayed absorbable materials could meet these requirements and poly-4-hydroxybutyrate (P4HB) might be such a new material for future pelvic floor implants. We studied in vitro bacterial adhesion and biofilm formation on P4HB in comparison to PP. We investigated the influence of both polymers using flat films and compared P4HB and PP implants with different knitting designs. P4HB flat films were demonstrated to be hydrophilic with significantly less Staphylococcus aureus and Escherichia coli cultured from P4HB films than from hydrophobic PP films after 24 h of incubation. On the implants, a higher number of E. coli were cultured after 1 h of incubation from the knitted P4HB implant with the highest density and smallest pore size, compared to other P4HB and PP implants. No differences were observed between the implants for E. coli at later time points or for S. aureus incubation. These results show that in flat films, the polymer influences biofilm formation, demonstrated by a reduced biofilm formation on P4HB compared with PP flat films. In addition, the knitting design may affect bacterial adhesion. Despite certain design and material characteristics that give the knitted P4HB implants a higher surface area, this did not result in more bacterial adhesion and biofilm formation overall. Collectively, these results warrant further (pre)clinical investigations of P4HB pelvic floor implants.

A Zebrafish Embryo Model for In Vivo Visualization and Intravital Analysis of Biomaterial-associated Staphylococcus aureus Infection.

Biomaterial-associated infection (BAI) is a major cause of the failure of biomaterials/medical devices. Staphylococcus aureus is one of the major pathogens in BAI. Current experimental BAI mammalian animal models such as mouse models are costly and time-consuming, and therefore not suitable for high throughput analysis. Thus, novel animal models as complementary systems for investigating BAI in vivo are desired. In the present study, we aimed to develop a zebrafish embryo model for in vivo visualization and intravital analysis of bacterial infection in the presence of biomaterials based on fluorescence microscopy. In addition, the provoked macrophage response was studied. To this end, we used fluorescent protein-expressing S. aureus and transgenic zebrafish embryos expressing fluorescent proteins in their macrophages and developed a procedure to inject bacteria alone or together with microspheres into the muscle tissue of embryos. To monitor bacterial infection progression in live embryos over time, we devised a simple but reliable method of microscopic scoring of fluorescent bacteria. The results from microscopic scoring showed that all embryos with more than 20 colony-forming units (CFU) of bacteria yielded a positive fluorescent signal of bacteria. To study the potential effects of biomaterials on infection, we determined the CFU numbers of S. aureus with and without 10 µm polystyrene microspheres (PS10) as model biomaterials in the embryos. Moreover, we used the ObjectJ project file "Zebrafish-Immunotest" operating in ImageJ to quantify the fluorescence intensity of S. aureus infection with and without PS10 over time. Results from both methods showed higher numbers of S. aureus in infected embryos with microspheres than in embryos without microspheres, indicating an increased infection susceptibility in the presence of the biomaterial. Thus, the present study shows the potential of the zebrafish embryo model to study BAI with the methods developed here.

In vitro methods for the evaluation of antimicrobial surface designs.

Bacterial adhesion and subsequent biofilm formation on biomedical implants and devices are a major cause of their failure. As systemic antibiotic treatment is often ineffective, there is an urgent need for antimicrobial biomaterials and coatings. The term "antimicrobial" can encompass different mechanisms of action (here termed "antimicrobial surface designs"), such as antimicrobial-releasing, contact-killing or non-adhesivity. Biomaterials equipped with antimicrobial surface designs based on different mechanisms of action require different in vitro evaluation methods. Available industrial standard evaluation tests do not address the specific mechanisms of different antimicrobial surface designs and have therefore been modified over the past years, adding to the myriad of methods available in the literature to evaluate antimicrobial surface designs. The aim of this review is to categorize fourteen presently available methods including industrial standard tests for the in vitro evaluation of antimicrobial surface designs according to their suitability with respect to their antimicrobial mechanism of action. There is no single method or industrial test that allows to distinguish antimicrobial designs according to all three mechanisms identified here. However, critical consideration of each method clearly relates the different methods to a specific mechanism of antimicrobial action. It is anticipated that use of the provided table with the fourteen methods will avoid the use of wrong methods for evaluating new antimicrobial designs and therewith facilitate translation of novel antimicrobial biomaterials and coatings to clinical use. The need for more and better updated industrial standard tests is emphasized. STATEMENT OF SIGNIFICANCE: European COST-action TD1305, IPROMEDAI aims to provide better understanding of mechanisms of antimicrobial surface designs of biomaterial implants and devices. Current industrial evaluation standard tests do not sufficiently account for different, advanced antimicrobial surface designs, yet are urgently needed to obtain convincing in vitro data for approval of animal experiments and clinical trials. This review aims to provide an innovative and clear guide to choose appropriate evaluation methods for three distinctly different mechanisms of antimicrobial design: (1) antimicrobial-releasing, (2) contact-killing and (3) non-adhesivity. Use of antimicrobial evaluation methods and definition of industrial standard tests, tailored toward the antimicrobial mechanism of the design, as identified here, fulfill a missing link in the translation of novel antimicrobial surface designs to clinical use.

The zebrafish embryo as a model to quantify early inflammatory cell responses to biomaterials.

To rapidly assess early inflammatory cell responses provoked by biomaterials in the full complexity of the living organism, we developed a zebrafish embryo model which allows real time analysis of these responses to biomaterial microspheres. Fluorescently labeled microspheres with different properties were injected into embryos of selected transgenic zebrafish lines expressing distinct fluorescent proteins in their neutrophils and macrophages. Recruitment of leukocytes and their interactions with microspheres were monitored using fluorescence microscopy. We developed a novel method using ImageJ and the plugin ObjectJ project file "Zebrafish-Immunotest" for rapid and semi-automated fluorescence quantification of the cellular responses. In the embryo model we observed an ordered inflammatory cell response to polystyrene and poly (ε-caprolactone) microspheres, similar to that described for mammalian animal models. The responses were characterized by an early infiltration of neutrophils followed by macrophages, and subsequent differentially timed migration of these cells away from the microspheres. The size of microspheres (10 and 15 µm) did not influence the cellular responses. Poly (ε-caprolactone) microspheres provoked a stronger infiltration of neutrophils and macrophages than polystyrene microspheres did. Our study shows the potential usefulness of zebrafish embryos for in vivo evaluation of biomaterial-associated inflammatory cell responses. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 2522-2532, 2017.

Selective laser melting porous metallic implants with immobilized silver nanoparticles kill and prevent biofilm formation by methicillin-resistant Staphylococcus aureus.

Implant-associated infection and limited longevity are two major challenges that orthopedic devices need to simultaneously address. Additively manufactured porous implants have recently shown tremendous promise in improving bone regeneration and osseointegration, but, as any conventional implant, are threatened by infection. In this study, we therefore used rational design and additive manufacturing in the form of selective laser melting (SLM) to fabricate porous titanium implants with interconnected pores, resulting in a 3.75 times larger surface area than corresponding solid implants. The SLM implants were biofunctionalized by embedding silver nanoparticles in an oxide surface layer grown using plasma electrolytic oxidation (PEO) in Ca/P-based electrolytes. The PEO layer of the SLM implants released silver ions for at least 28 days. X-ray diffraction analysis detected hydroxyapatite on the SLM PEO implants but not on the corresponding solid implants. In vitro and ex vivo assays showed strong antimicrobial activity of these novel SLM PEO silver-releasing implants, without any signs of cytotoxicity. The rationally designed SLM porous implants outperformed solid implants with similar dimensions undergoing the same biofunctionalization treatment. This included four times larger amount of released silver ions, two times larger zone of inhibition, and one additional order of magnitude of reduction in numbers of CFU in an ex vivo mouse infection model.

A doxycycline-loaded polymer-lipid encapsulation matrix coating for the prevention of implant-related osteomyelitis due to doxycycline-resistant methicillin-resistant Staphylococcus aureus.

Implant-associated bone infections caused by antibiotic-resistant pathogens pose significant clinical challenges to treating physicians. Prophylactic strategies that act against resistant organisms, such as methicillin-resistant Staphylococcus aureus (MRSA), are urgently required. In the present study, we investigated the efficacy of a biodegradable Polymer-Lipid Encapsulation MatriX (PLEX) loaded with the antibiotic doxycycline as a local prophylactic strategy against implant-associated osteomyelitis. Activity was tested against both a doxycycline-susceptible (doxy(S)) methicillin-susceptible S. aureus (MSSA) as well as a doxycycline-resistant (doxy(R)) methicillin-resistant S. aureus (MRSA). In vitro elution studies revealed that 25% of the doxycycline was released from the PLEX-coated implants within the first day, followed by a 3% release per day up to day 28. The released doxycycline was highly effective against doxy(S) MSSA for at least 14days in vitro. A bolus injection of doxycycline mimicking a one day release from the PLEX-coating reduced, but did not eliminate, mouse subcutaneous implant-associated infection (doxy(S) MSSA). In a rabbit intramedullary nail-related infection model, all rabbits receiving a PLEX-doxycycline-coated nail were culture negative in the doxy(S) MSSA-group and the surrounding bone displayed a normal physiological appearance in both histological sections and radiographs. In the doxy(R) MRSA inoculated rabbits, a statistically significant reduction in the number of culture-positive samples was observed for the PLEX-doxycycline-coated group when compared to the animals that had received an uncoated nail, although the reduction in bacterial burden did not reach statistical significance. In conclusion, the PLEX-doxycycline coating on titanium alloy implants provided complete protection against implant-associated MSSA osteomyelitis, and resulted in a significant reduction in the number of culture positive samples when challenged with a doxycycline-resistant MRSA.

Critical factors in the translation of improved antimicrobial strategies for medical implants and devices.

Biomaterials-associated infection incidence represents an increasing clinical challenge as more people gain access to medical device technologies worldwide and microbial resistance to current approaches mounts. Few reported antimicrobial approaches to implanted biomaterials ever get commercialized for physician use and patient benefit. This is not for lack of ideas since many thousands of claims to new approaches to antimicrobial efficacy are reported. Lack of translation of reported ideas into medical products approved for use, results from conflicting goals and purposes between the various participants involved in conception, validation, development, commercialization, safety and regulatory oversight, insurance reimbursement, and legal aspects of medical device innovation. The scientific causes, problems and impressive costs of the limiting clinical options for combating biomaterials-associated infection are well recognized. Demands for improved antimicrobial technologies constantly appear. Yet, the actual human, ethical and social costs and consequences of their occurrence are less articulated. Here, we describe several clinical cases of biomaterials-associated infections to illustrate the often-missing human elements of these infections. We identify the current societal forces at play in translating antimicrobial research concepts into clinical implant use and their often-orthogonal constituencies, missions and policies. We assert that in the current complex environment between researchers, funding agencies, physicians, patients, providers, producers, payers, regulatory agencies and litigators, opportunities for translatable successes are minimized under the various risks assumed in the translation process. This argues for an alternative approach to more effectively introduce new biomaterials and device technologies that can address the clinical issues by providing patients and medical practitioners new options for desperate clinical conditions ineffectively addressed by biomedical innovation.

Persistence of a bioluminescent Staphylococcus aureus strain on and around degradable and non-degradable surgical meshes in a murine model.

Biomaterials are increasingly used for the restoration of human function, but can become infected as a result of peri- or early post-operative bacterial contamination, although biomaterial-associated infections (BAIs) can also initiate at any time from hematogenous spreading of bacteria from an infection elsewhere in the body. Infecting bacteria in BAIs not only seek shelter in their own protective biofilm matrix, but also hide in surrounding tissue. This study compares staphylococcal persistence on and around a degradable and non-degradable surgical mesh through the use of longitudinal bioluminescence imaging in a murine model, including histological evaluation of surrounding tissue after sacrifice. Surgical meshes were first contaminated with bioluminescent Staphylococcus aureus Xen29 and subsequently subcutaneously implanted in mice. Bioluminescent staphylococci persisted on and around non-degradable meshes during the 28-day course of the study, whereas bioluminescence returned to control levels and bacteria disappeared from surrounding tissues once a degradable mesh had fully dissolved. Thus the application of degradable biomaterials yields major advantages with respect to the prevention of BAIs, as dissolution of the implant not only is associated with elimination of the protective biofilm mode of growth of the infecting organisms, but also allows the immune system to clear the surrounding tissue from infecting organisms.

Biomaterial-associated infection: locating the finish line in the race for the surface.

Biomaterial-associated infections occur on both permanent implants and temporary devices for restoration or support of human functions. Despite increasing use of biomaterials in an aging society, comparatively few biomaterials have been designed that effectively reduce the incidence of biomaterial-associated infections. This review provides design guidelines for infection-reducing strategies based on the concept that the fate of biomaterial implants or devices is a competition between host tissue cell integration and bacterial colonization at their surfaces.

In vitro antibacterial activity of porous TiO2-Ag composite layers against methicillin-resistant Staphylococcus aureus.

The aim of this study was the synthesis of a porous TiO(2)-Ag composite coating and assessment of its in vitro bactericidal activity against methicillin-resistant Staphylococcus aureus. The coating was produced by plasma electrolytic oxidation of Ti-6Al-7Nb medical alloy in a calcium acetate/calcium glycerophosphate electrolyte bearing Ag nanoparticles. Following oxidation, the surface of the titanium substrate was converted into the corresponding oxide (TiO(2)) bearing Ca and P species from the electrolyte. In addition, Ag was detected associated with particles present in the oxide layers. The coatings revealed a porous interconnected structure with pores up to 3 microm in size, a threefold increase in roughness and improved wettability relative to the non-oxidized specimens. The composite TiO(2)-Ag coating showed complete killing of methicillin-resistant S. aureus within 24h in all culture conditions, whereas a 1000-fold increase in bacterial numbers was recorded with the ground titanium specimens and the samples oxidized in the absence of Ag nanoparticles.

The influence of antibodies on Staphylococcus epidermidis adherence to polyvinylpyrrolidone-coated silicone elastomer in experimental biomaterial-associated infection in mice.

Biomaterial-associated infection (BAI) is a major problem in modern medicine, and is often caused by Staphylococcus epidermidis. We aimed to raise monoclonal antibodies (mAbs) against major surface protein antigens of S. epidermidis, and to assess their possible protective activity in experimental BAI. Mice were vaccinated with a cell wall protein preparation of S. epidermidis. A highly immunodominant antigen was identified as Accumulation-associated protein (Aap). mAbs against Aap and against surface-exposed lipoteichoic acid (LTA) were used for passive immunization of mice in experimental biomaterial-associated infection. Neither anti-Aap nor anti-LTA mAbs showed protection. Either with or without antibodies, tissue surrounding the implants was more often culture positive than the implants themselves, but bacterial adherence to the implants was significantly increased in mice injected with anti-LTA. In vitro, anti-Aap and anti-LTA did show binding to S. epidermidis, but no opsonic activity was observed. We conclude that antibodies against S. epidermidis LTA or Aap showed no opsonic activity and did not protect mice against BAI. Moreover, the increase in binding to implanted biomaterial suggests that passive immunization may increase the risk for BAI.

Peri-implant tissue is an important niche for Staphylococcus epidermidis in experimental biomaterial-associated infection in mice.

Biomaterial-associated infections (BAI), which are predominantly caused by Staphylococcus epidermidis, are a significant problem in modern medicine. Biofilm formation is considered the pivotal element in the pathogenesis, but in previous mouse studies we retrieved S. epidermidis from peri-implant tissue. To assess the kinetics and generality of tissue colonization, we investigated BAI using two S. epidermidis strains, two biomaterials, and two mouse strains. With small inocula all implants were culture negative, whereas surrounding tissues were positive. When higher doses were used, tissues were culture positive more often than implants, with higher numbers of CFU. This was true for the different biomaterials tested, for both S. epidermidis strains, at different times, and for both mouse strains. S. epidermidis colocalized with host cells at a distance that was >10 cell layers from the biomaterial-tissue interface. We concluded that in mouse experimental BAI S. epidermidis peri-implant tissue colonization is more important than biofilm formation.