Silver. I: Its antibacterial properties and mechanism of action

Antifungal and antibacterial properties of a silver-loaded cellulosic fiber

The skin is the interface between the body and the environment. Each skin type has a specific skin physiology and is more or less adapted for protection against multiple stress factors. Textiles on the other hand are the tissues with the longest contact to the human skin. They play a critical role especially in skin conditions with an increased rate of bacterial and fungal infections like atopic dermatitis and hyperhidrosis, and in diabetic patients and aged skin. The present study demonstrates the antifungal and antibacterial effects of SeaCell Active in an in vitro test system against Candida albicans (DSM 11225), Candida tropicalis (ATCC 1169), and Candida krusei (ATCC 6258). Furthermore, the antibacterial activity of fibers with different amounts of SeaCell Active fibers in a dose-dependent manner against Staphylococcus aureus (ATCC 22923) and Escherichia coli (ATCC 35218) could be demonstrated. If this fiber seems to be suited for bioactive textiles in specific anatomical regions and skin conditions with a susceptibility for fungal and bacterial infections due to Candida species, namely Staphylococcus aureus and Escherichia coli, must be examined by means of further investigations, especially in vivo tests in human, considering allergic and toxic effects of the fiber.

Antimicrobial activities of silver dressings: an in vitro comparison

A range of silver-coated or -impregnated dressings are now commercially available for use but comparative data on their antimicrobial efficacies are limited. The antibacterial activities of five commercially available silver-coated/impregnated dressings were compared against nine common burn-wound pathogens, namely methicillin-sensitive and -resistant Staphylococcus aureus (MRSA), Enterococcus faecalis, Pseudomonas aeruginosa, Escherichia coli, Enterobacter cloacae, Proteus vulgaris, Acinetobacter baumannii and a multi-drug-efflux-positive Acinetobacter baumannii (BM4454), using a broth culture method. The rapidity and extent of killing of these pathogens under in vitro conditions were evaluated. All five silver-impregnated dressings investigated exerted bactericidal activity, particularly against Gram-negative bacteria, including Enterobacter species, Proteus species and E. coli. The spectrum and rapidity of action, however, ranged widely for different dressings. Acticoat and Contreet had a broad spectrum of bactericidal activities against both Gram-positive and -negative bacteria. Contreet was characterized by a very rapid bactericidal action and achieved a reduction of ⩾10 000 c.f.u. ml−1 in the first 30 min for Enterobacter cloacae, Proteus vulgaris, Pseudomonas aeruginosa and Acinetobacter baumanii. Other dressings demonstrated a narrower range of bactericidal activities. Understanding the characteristics of these dressings may enable them to be targeted more appropriately according to the specific requirements for use of a particular dressing, as in for prophylaxis in skin grafting or for an infected wound with MRSA.

Nanocrystalline silver dressings in wound management: a review

This paper describes the properties of nanocrystalline silver products (Acticoat) and their applications and examines available evidence supporting their use in wound management. Acticoat utilizes nanotechnology to release nanocrystalline silver crystals. Acticoat releases 30 times less silver cations than silversulfadiazine cream or 0.5% silver nitrate solution but more of the silver released (by Acticoat). Silver-impregnated slow-release dressings release minute concentrations of silver which are quickly bound up by the chloride in the wound exudate. While extrapolations from in vitro and animal studies are cautious, evidence from these studies suggests Acticoat is: effective against most common strains of wound pathogens; can be used as a protective covering over skin grafts; has a broader antibiotic spectrum activity; and is toxic to keratinocytes and fibroblasts. Animal studies suggest a role for nanocrystalline silver in altering wound inflammatory events and facilitation of the early phase of wound healing. Quality human clinical trials into nanocrystalline silver are few. However, evidence suggests using Acticoat in wound management is cost effective, reduces wound infection, decreases the frequency of dressing changes and pain levels, decreases matrix metalloproteinase activity, wound exudate and bioburden levels, and promotes wound healing in chronic wounds. Although there is no in vivo evidence to suggest nanocrystalline silver is toxic to human keratinocytes and fibroblasts, there is in vitro evidence to suggest so; thus these dressings should be used cautiously over epithelializing and proliferating wounds. Future clinical research, preferably randomized controlled trials into nanocrystalline silver technology, may provide clinicians a better understanding of its applications in wound management.

The management of malodour and exudate in fungating wounds

The topic of malodour and exudate in fungating wounds is of particular interest and relevance for community nurses who care for patients with fungating wounds in the community setting. Community nurses can work together with community oncology and palliative care services to manage patients with fungating wounds at home, where once hospital admission would have been needed to provide the level of support and care these patients require. Fungating wounds present unique challenges and can be problematic as a result of the levels of exudate and malodour which they produce. This review sought to establish whether recent advances in wound care products and/or techniques, could be of value in the control of these symptoms. The review established that there is little clinical research into the care of fungating wounds, and that the development of new dressings and techniques for controlling malodour and exudate is badly needed.

A silver coated dressing reduces the incidence of early burn wound cellulitis and associated costs of inpatient treatment: Comparative patient care audits

In 2000 and 2002, the Royal Perth Hospital (RPH) Burn Unit, Western Australia, conducted two 'before and after' patient care audits comparing the effectiveness and cost of Silvazine (silver sulphadiazine and chlorhexidine digluconate cream) and Acticoat, a new dressing product for in-patient treatment of early burn wounds. The main outcome variables were: burn wound cellulitis, antibiotic use and cost of treatment. Two patient care audits and a comparative sample were used. The two regimes audited were, 'standard treatment' of twice daily showers or washes with 4% chlorhexidine soap and Silvazine cream as a topical dressing (2000, n=51), compared with the 'new treatment' of daily showers of the burn wound with 4% chlorhexidine soap and the application of an Acticoat dressing (2002, n=19). In 2002, costs were also examined using a sample of matched pairs (n=8) of current and previous patients. The main findings were: when using Acticoat the incidence of infection and antibiotic use fell from 55% (28/51) and 57% (29/51) in 2000 to 10.5% (2/19) and 5.2% (1/19) in 2002. The total costs (excluding antibiotics, staffing and surgery) for those treated with Silvazine were US$ 109,357 and those treated with Acticoat were US$ 78,907, demonstrating a saving of US$ 30,450 with the new treatment. The average length of stay (LOS) in hospital was 17.25 days for the Silvazine group and 12.5 days for the Acticoat group-a difference of 4.75 days. These audits demonstrate that Acticoat results in a reduced incidence of burn wound cellulitis, antibiotic use and overall cost compared to Silvazine in the treatment of early burn wounds.

Silver absorption and antibacterial efficacy of silver dressings

OBJECTIVE

To evaluate the patterns of silver release from selected sustained silver-release dressings and the protective role of proteins in wound exudate and wound scale. The bactericidal action of silver in chronic wound therapy is also examined.

METHOD

Sequential microbiological examination of wound swabs from seven patients with chronic wounds and sampling of wound exudate and wound scale. Silver content was measured using atomic absorption spectrometry. The ability of Contreet Foam to absorb exudate and release silver was studied in punch biopsy wounds in a rodent model.

RESULTS

Silver accumulation in wound exudate correlated well with its viscosity and protein content. Silver bound to wound scale and debris was approximately proportional to the silver ion release from dressings. Bacterial burden was controlled, but not eliminated, following chronic silver therapy.

CONCLUSION

Silver dressings (Acticoat-7, Actisorb Silver, Contreet Foam, Aquacel Ag and Flamazine) were found to be safe for use in chronic wound therapy. Excess silver ion is bound by wound exudate and wound scale as a protective mechanism. Silver-release dressings are not likely to result in germ-free wounds. Further studies are needed to examine potential silver resistance.

Photodynamic therapy for Staphylococcus aureus infected burn wounds in mice

The rise of multiply antibiotic resistant bacteria has led to searches for novel antimicrobial therapies to treat infections. Photodynamic therapy (PDT) is a potential candidate; it uses the combination of a photosensitizer with visible light to produce reactive oxygen species that lead to cell death. We used PDT mediated by meso-mono-phenyl-tri(N-methyl-4-pyridyl)-porphyrin (PTMPP) to treat burn wounds in mice with established Staphylococcus aureus infections The third degree burn wounds were infected with bioluminescent S. aureus. PDT was applied after one day of bacterial growth by adding a 25% DMSO/500 microM PTMPP solution to the wound followed by illumination with red light and periodic imaging of the mice using a sensitive camera to detect the bioluminescence. More than 98% of the bacteria were eradicated after a light dose of 210 J cm(-2) in the presence of PTMPP. However, bacterial re-growth was observed. Light alone or PDT both delayed the wound healing. These data suggest that PDT has the potential to rapidly reduce the bacterial load in infected burns. The treatment needs to be optimized to reduce wound damage and prevent recurrence.

Vascular graft infections:In vitro andin vivo investigations of a new vascular graft with long-term protection

We investigated a polyester vascular prosthesis (PET) coated with elemental silver (SC). Measurement of silver release over a period of 52 weeks by means of inductively coupled plasma atomic emission spectrometry of PET with (PET-G) and without (PET-N) gelatine impregnation revealed a silver release on the first day of 1.2 +/- 0.2 microg (PET-N) and 1.2 +/- 0.1 microg (PET-G) (calculated for 1 g of prosthesis); from the 90th day onward, it was between 0.22 +/- 0.14 microg (PET-N) and 0.18 +/- 0.12 microg (PET-G) per day. The prostheses were incubated with Staphylococcus aureus (S.a.), Staphylococcus epidermidis (S.e.), or Escherichia coli (E.c.) to investigate in vitro antibacterial efficacy. After 6 h of incubation, no colony-forming units were to be seen for any of the bacterial suspensions for PET with SC (p < 0.001). To investigate in vivo antibacterial efficacy, PET-G rings with and without SC contaminated with S.a., S.e., or E.c. were implanted in 18 albino rabbits and examined 7 days after agar culture for 48 h. The silver coating was associated with a significant reduction in bacterial growth (S.a., p = 0.001; S.e., p < 0.005; E.c., p < 0.001). The silver-coated prosthesis, with and without gelatine impregnation, had a significantly antibacterial effect with continuous release of silver.

Colloidal silver as an antimicrobial agent: fact or fiction?

OBJECTIVE

Colloidal silver preparations are marketed on the internet as omnipotent antimicrobial agents, but scientific support for these claims is lacking. This study reports the results of in vitro tests of colloidal silver's antimicrobial activity against several pathogenic or non-pathogenic microorganisms.

METHOD

Three samples of colloidal silver were tested: one available commercially on the internet (silver concentration of 22 ppm) and two samples (concentrations of 403 and 413 ppm) which were prepared in our laboratory using standard chemical methods.

RESULTS

In an agar-well diffusion assay none of the three colloidal silver solutions had any effect on the growth of the test organisms. All tested bacterial strains were sensitive to ciprofloxacin. Colloidal silver 22 ppm showed no bactericidal activity in phenol coefficient tests.

CONCLUSION

As the tested colloidal silver solutions did not show any antimicrobial effect in vitro on the microorganisms, claims of colloidal silver's antimicrobial potency are misleading and there is no place for it as an antiseptic.

A review of the use of silver in wound care: facts and fallacies

This review traces the use of silver in wound care, discussing its merits as an antibacterial agent and constituent of many new dressings, which are increasingly tailored to the treatment of wounds ranging from acute surgical lesions to chronic and diabetic leg ulcers. Misconceptions regarding the biological properties of silver, its possible physiological value in the human body and wound bed, absorption through the skin, and safety factors are addressed. The article aims to present silver and the new range of sustained silver-release dressings as important features in the management of skin wounds, providing effective control of wound infections while ensuring patient comfort and quality of life.

Controlling wound bioburden with a novel silver-containing HydrofiberR dressing

Clinicians now recognize that both aerobic and anaerobic microorganisms have the ability to degrade or damage host tissue at a wound site through the production of a variety of enzymes and toxins. Silver-containing dressings offer one method for controlling this polymicrobial wound bioburden, and research efforts are currently ongoing to determine their efficacy against aerobic, anaerobic, and antibiotic-resistant microorganisms. The current study aimed to determine the antimicrobial activity of a new silver-containing Hydrofiber dressing (AQUACEL Ag) on both aerobic and anaerobic microorganisms, using the zone-of-inhibition method. This method provides a measure of the ability of the dressing to make available a sufficient concentration of silver to have an antimicrobial effect. To some extent this test mimics the clinical use of the dressing and predicts its microbicidal activity at the wound-dressing interface. The results show that the silver-containing dressing makes silver available at a dressing-agar interface at a concentration that is effective against a broad range of aerobic, anaerobic, and antibiotic-resistant microorganisms. In the context of wound healing, the results showing antimicrobial activity against antibiotic-resistant microorganisms are particularly important, as the control and eradication of these organisms is a major concern within the health care profession.

Understanding exudate management and the role of exudate in the healing process

Studies suggest that wound fluid from acute wounds may have a beneficial effect on wound healing, whereas that of chronic wounds may inhibit healing. Changes in the volume and nature of exudate provide information on the underlying state of the wound and may give an indication of an increasing bacterial load and the presence of infection, and if a wound is likely to proceed to healing. Careful monitoring of the exudate can provide information for the application of systemic and local therapies. Individual wound care products have specific functions which relate to the volume, viscosity and nature of the exudate and these should guide skin care and dressing selection.

Development and characterisation of silver-doped bioactive glass-coated sutures for tissue engineering and wound healing applications

A novel silver-doped bioactive glass powder (AgBG) was used to coat resorbable Vicryl (polyglactin 910) and non-resorbable Mersilk surgical sutures, thereby imparting bioactive, antimicrobial and bactericidal properties to the sutures. Stable and homogeneous coatings on the surface of the sutures were achieved using an optimised aqueous slurry-dipping technique. Dynamic mechanical analysis (DMA) was used to investigate the viscoelastic parameters of storage modulus and tandelta and thermal transitions of the as-received and composite (coated) sutures. The results generally showed that the bioactive glass coating did not affect the dynamic mechanical and thermal properties of the sutures. The in vitro bioactivity of the sutures was tested by immersion in simulated body fluid (SBF). After only 3 days of immersion in SBF, bonelike hydroxyapatite formed on the coated suture surfaces, indicating their enhanced bioactive behaviour. Resorbable sutures with bioactive coatings as fabricated here, in conjunction with 3-D textile technology, may provide attractive materials for producing 3-D scaffolds with controlled porosities for tissue engineering applications. The bactericidal properties imparted by the Ag-containing glass coating open also new opportunities for use of the composite sutures in wound healing and body wall repair.

Plastic Surgery

The range of casualties treated by the Defence Medical Services in the recent Gulf conflict has reaffirmed the important role of plastic surgery within the military. This review seeks to highlight some areas of recent innovation and improvement within the realms of plastic surgery generally, of which some, such as the introduction of Flammacerium and the availability of skin substitutes, have direct military relevance.

Aquacel Ag?? in the Management of Partial-Thickness Burns: Results of a Clinical Trial

Aquacel Hydrofiber is a moisture retentive topical dressing that has been demonstrated to be safe and efficacious for the management of partial-thickness burns, showing parity for most dressing related aspects to cadaver skin for this indication. Recently, 1.2% w/w silver has been added to the Aquacel Hydrofiber, to create Aquacel Ag. This new material releases silver within the dressing for up to two weeks, and it is this duration that differentiates it from other sustained release silver delivery products indicated for burn management. The dressing was tested in a phase II noncomparative trial in superficial, mid dermal, and mixed partial-thickness burns. Percentage and speed of reepithelialization were satisfactory and appear to be similar at least to results noted with silver sulfadiazine, although, no direct comparisons were performed in this study. Pain reduction between baseline and postburn day number three and five was statistically significant. Conformability, general ease of use and other functional dressing properties were rated very positively. Overall, Aquacel Ag combines several properties known to be beneficial for the management of partial-thickness burns and is a very good choice for superficial and mid-thickness burn injuries.

An overview of Acticoat dressing in wound management

This article reviews the in vitro and in vivo studies available on a new nanocrystalline silver dressing, Acticoat (Smith & Nephew), and discusses their relevance to the availability of this product on the Drug Tariff. The addition of nanocrystalline silver dressings will make a valuable contribution to wound care in the community, in terms of providing continuity of care for patients who are discharged from hospital and also in preventing admission to hospital with non-manageable wound infection.

Clinical performance of a new silver dressing, Contreet Foam, for chronic exuding venous leg ulcers

OBJECTIVE

This study aimed to evaluate the safety and performance of a new sustained silver-releasing dressing, Contreet Foam (Coloplast A/S), in the treatment of moderately to highly exuding chronic venous leg ulcers in which healing is delayed due to the presence of bacteria.

METHOD

The clinical performance of Contreet Foam was studied for four weeks in 25 patients with moderately to highly exuding delayed-healing venous leg ulcers. Healing was assessed on a weekly basis with reference to the wound-bed tissue composition, degree of odour and pain, dressing performance and the dressing's effect on the peri-ulcer area. Blood samples were analysed for silver content.

RESULTS

Twenty-three out of 25 patients completed the study. One ulcer healed and no wound infections occurred during the study period. A mean 56% reduction in ulcer area (from 15.6 to 6.9 cm2) was recorded during the four weeks, and there was a mean 25% reduction in granulation tissue from dull to healthy after one week. Wound odour reduced significantly after one week. Mean dressing wear time was 3.1 days, and there were only minimal incidences of leakage. Serum silver levels did not exceed reference values.

CONCLUSION

Contreet Foam was found to be safe and performed well when used in the treatment of delayed-healing chronic venous leg ulcers, combining effective antibacterial properties with excellent exudate management.

DECLARATION OF INTEREST

This study was supported by Coloplast A/S, Humlebaek, Denmark.

Treatment of an atypical leg ulcer: pyoderma gangrenosum

Mrs B was referred to the Skin and Woundcare Department at the start of January 2002 with a chronic non-healing ulcer to her lower right leg proximal to the medial aspect of her right knee. The ulcer was diagnosed as pyoderma gangrenosum, a condition which Mrs B had suffered from previously. Assessment and management of this atypical ulcer are discussed. Once the progression of the lesion was halted, conservative treatment could be undertaken, and led to a successful outcome.

Management of toxic epidermal necrolysis in a 15-year-old girl

Toxic epidermal necrolysis, a life-threatening reaction to certain types of drugs, is characterised by epidermal sloughing of more than 30% of the total body surface area. Patient survival depends on prompt referral to a specialist burns unit.

A comparison of the antimicrobial effects of four silver-containing dressings on three organisms

OBJECTIVE

To compare the antimicrobial activity of four silver-containing dressings: Acticoat (Smith and Nephew), Actisorb Silver 220 (Johnson and Johnson), Avance (SSL International) and Contreet-H (Coloplast).

METHOD

The dressings were tested against three micro-organisms: a Gram-positive bacterium, Staphylococcus aureus; a Gram-negative organism, Escherichia coli; and a yeast, Candida albicans, using three different techniques. Each dressing also had its silver content analysed.

RESULTS

Acticoat is likely to produce the most rapid antimicrobial effect in vitro because of the rapid release of relatively large concentrations of highly active silver ions. Contreet-H has broadly similar antimicrobial activity to Acticoat, but has a slower onset of action. Actisorb Silver 220 appears to offer less prospect of killing bacteria within the wound itself, but the dressing is capable of removing micro-organisms from wound exudate and sequestering them until they are inactivated by the silver within the charcoal fibres. Little convincing evidence for any antimicrobial activity of Avance was found.

CONCLUSION

Although caution must always be exercised when extrapolating the results of laboratory-based studies to the clinical situation, potentially important differences were detected in the antimicrobial activity of the four products examined. It is also possible that the silver ions released by the dressings may have effects on wound healing that are unrelated to their antimicrobial activity. Further work is needed to address this issue.

A reappraisal of the role of cerium in burn wound management

A rare earth element, cerium, was introduced as an antibacterial agent in 1976 but has rarely been used due to the emphasis on wound excision. Used in combination with silver sulphadiazine, it may improve patient survival when excision is not possible.

Controversies over colloidal silver

Colloidal silver was introduced into skin care more than 60 years ago, when the antiseptic action of higher concentrations of silver nitrate was deemed unacceptable on account of their irritancy and astringency.

Silver. 2: Toxicity in mammals and how its products aid wound repair

The second article examining the role of this metallic element in a wound environment discusses toxicity in individual cells, animals and humans and considers how different silver-based dressings assist in wound healing.

Wound pathophysiology, infection and therapeutic options

Wound healing is a complex and highly regulated process that can be compromised by both endogenous factors (pathophysiological) and exogenous factors (micro-organisms). Microbial colonisation of both acute and chronic wounds is inevitable, and in most situations endogenous bacteria predominate, many of which are potentially pathogenic in the wound environment. The risk of wound infection increases as local conditions favour bacterial growth rather than host defence. Consequently a primary objective in wound management is to redress the host-bacterial balance, and this is most effectively achieved by ensuring that the wound is cleared of devitalised tissue and foreign bodies, the bacterial load and inflammation are controlled, and that adequate tissue perfusion is maintained. Although surgical debridement is the most rapid and effective technique for removing devitalised tissue, topical enzymes, moisture-retentive dressings, biosurgical therapy and vacuum therapy have been used as alternative approaches to wound cleansing and preparation. Topical antimicrobial agents continue to be used widely for preventing wound infection and current interest is focused on alternatives to antibiotics, such as antimicrobial moisture-retentive dressings, honey, essential oils and cationic peptides. In addition to the need to control wound microflora, unregulated inflammation caused by both micro-organisms and underlying abnormal pathophysiological conditions is a major factor associated with poor healing in chronic wounds. Consequently, therapeutic strategies that target chronic inflammatory processes are critical to wound progression. The success of future therapies will be dependent on a growing understanding of the pathophysiological processes and the host-bacterial interactions that significantly influence wound healing.