Clinical REVIEW

Pin and needle tract infection:

the prophylactic role of silver
Silver is widely used in wound dressings and medical devices to control pathogenic infections
which are recognised as causes of impaired healing, functional defects in orthopaedic fixation pins
and patient distress. This review discusses new approaches and advances in silver technology in
controlling infections associated with wound sutures, insertion points and in-dwelling catheters,
gastonomy tubes and orthopaedic fixation pins. The author discusses silver-coated and silver-
containing sutures and considers efficacy, safety in use and the possibility of silver resistance.

Alan BG Lansdown

dressings that release silver ions in for intravascular, intraperitoneal

KEY WORDS the presence of moisture and wound or suprapubic insertion and other
Silver technology exudates (Lansdown, 2002a,b; 2005). devices for surgical intervention are
not currently available in the UK at
Skin wounds Silver has a proven efficacy against the present time, but are subject to
Silver a wide spectrum of bacteria, fungi research in the USA and in other parts
Medical devices and yeasts and various dressings, of Europe. A survey of the literature
Sutures which have been tailored to treat reveals three main lines of research
specific wound types, provide great into the control of infections associated
advantages in the management of with surgical incisions, medical devices
heavily exudating ulcers, malodorous and other surgical interventions:

S
kin wounds vary greatly in their conditions and patient discomfort 8 The use of metallic silver in surgical
causation, severity, pathological (Ovington, 2001; White, 2001). knives, sutures and orthopaedic
characteristics and capacity Whereas the literature is replete pins
to heal (Grey and Harding, 1998; with highly relevant information on 8 Topical application of silver nitrate,
Dow et al,1999; Bowler, 2003). All the value of silver in treating chronic silver sulphadiazine or silver ion
wounds breaching the epidermal wounds and burns, less attention release dressings to wound sites
barrier function are prone to infection has been placed on its value in 8 Silver coating of materials used in
from opportunist pathogens from a controlling infections associated the manufacture of medical devices.
patient’s own body flora and from with wound suture insertion and
the nosocomial environment. Current sites of percutaneous penetration of In each case, the ionised silver
views on wound repair and tissue medical devices including in-dwelling released is highly reactive and readily
regeneration focus increasingly upon catheters, external fixation pins used in binds tissue debris, albumins, macro-
appropriate wound bed preparation orthopaedic surgery and acupuncture globulins and proteins in wound exudates
with elimination of pathogenic needles. Many infections commonly and tissue secretions. It interacts with
infections and establishment of an encountered in wound care may receptors on cell membranes and is
appropriate bacterial balance (Enoch colonise penetration sites and lead metabolised and possibly mobilised
and Harding, 2003; Schultz et al, 2003). to biofilm formation (Donlon, 2002; as a complex with metallothionein or
Considerable emphasis has been Dunne, 2002). Biofilms are a recurrent other metal binding proteins (Lansdown,
placed upon the prophylactic value of problem in the use of medical devices, 2002a), with a small proportion reaching
silver, silver sulphadiazine and wound especially catheters where they can the systemic circulation. Unbound silver
lead to functional impairment and ion is available for antimicrobial action
severe discomfort for the patient either through liberation into the wound
(Elliott, 1999; Saint et al, 2002). bed (Acticoat®, Smith & Nephew, Hull;
Alan BG Lansdown is Honorary Senior Research Fellow Urgotul®, Urgo, Chenôve) or within the
and Senior Lecturer in Chemical Pathology, Clinical Silver-coated external fixation dressing as in Aquacel® Ag (ConvaTec,
Chemistry, Investigative Sciences, Charing Cross pins, percutaneous enterostomal Ickenham) or Contreet® Foam
Campus, Imperial College Faculty of Medicine, London gastronomy (PEG) devices, catheters (Coloplast, Peterborough).

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 Product REVIEW
Clinical REVIEW

Silver ions released from topical efficacious action in heavily infected gastronomy devices and suprapubic
applications can be expected to control conditions (Burrell, 2003; 2004). drainage with sustained silver release
mainly superficial infections whereas dressings, tracheostomy and so on,
silver or silver-coated sutures, catheters, Inorganic salts of silver, especially few cases of infections have actually
fixation pins, screws and surgical nitrate, are astringent and irritant been reported. Leak (2002) drew
needles, should release biologically but show antiseptic effects. Lowbury attention to infections associated
active ions through the entire depth (1972) used 0.5% silver nitrate to with profound granulation and high
of the incision or device tract, to reduce Pseudomonas aeruginosa levels of exudate at percutaneous
control deeper infections. Ideally, silver infection in patients with burn wounds endoscopic gastrostomy (PEG) sites
used in the construction of medical from about 70% to 3%. Silver nitrate and how they can be effectively treated
devices will release silver ions for the is still used to control life-threatening with sustained silver-release dressings
entire duration of use. This article infections including P. aeruginosa and such as Actisorb Silver 220 (Johnson
will discuss clinical and experimental Staphylococcus aureus in burn wounds, & Johnson Wound Management,
evidence for the antimicrobial efficacy but its irritancy and astringency would Ascot). In Leak’s opinion, the inherent
of silver and silver-coated devices in preclude its routine use in disinfecting risks of superinfection, sensitisation
controlling percutaneous infections. superficial wounds associated with in- and emergence of antibiotic-resistant
Since ‘implantation’ of silver in the body dwelling catheters or other medical strains precluded the routine use of
in medical devices is liable to lead to devices. The caustic properties of antibiotics in the treatment of colonised
higher blood silver levels (argyraemias), silver nitrate are now licensed by the or infected wounds. On the other hand,
emphasis is placed upon safety in use of Medicines Control Agency (UK) as sustained silver ion release dressings are
silver or silver-coated medical devices. toughened silver nitrate for removal convenient to apply, safe and effective in
of warts, verrucae and unsightly controlling bacterial balances, malodours
Silver in controlling superficial granulations (Avoca®, Bray Healthcare, and resulting inflammatory changes
infections at device insertion sites Faringdon). It recommends extreme in surrounding skin (Lansdown and
Historically, silver has made caution when applying the preparation. Williams, 2004; Lansdown et al, 2005).
many contributions in controlling The manufacturers claim that silver In a pilot study, Leak (2002) successfully
postoperative infection in surgical nitrate fused with potassium nitrate employed Actisorb Silver 220 to treat
wounds. Silver surgical knives appear in in the form of a caustic pencil is safer PEG site infections where prolonged
historical collections and records exist and less painful for patients than more pressures and excessive exudates had
of silver needles, silver thread and silver corrosive or systemically administered led to some maceration. The practice
prostheses in early medicine. Ambrose therapies. It has been used effectively is now more widely adopted in the
Paré (1517–90) used silver clips in facial in the author’s clinic at Charing Cross Doncaster Royal Infirmary where the
reconstruction, and William Halstead Hospital to treat a local infection pilot study was carried out.
(1895) employed silver wire sutures in associated with a protruding bone
surgery for hernias. He recorded that fragment (Figure 1). (The silver deposits As an alternative to treating PEG
silver foil provided an effective barrier appear as blackish discolourations.) or catheter exit sites with silver
against postoperative infections. Other dressings earlier studies evaluated
early studies concluded that since silver While it may be common practice the use of silver cuffs located around
nitrate readily formed precipitates with in many clinics to treat infections at the devices at the points of entry or
albumin and sodium chloride, its local sites of insertion of intravascular or subcutaneously (Figure 2). Große-
action as an astringent and antibiotic intraperitoneal catheters, enterostomal Siestrup et al (1992) conducted a
could be readily controlled (Lubinski, clinical study of 20 patients implanted
1914). Lubinski (1914) considered with peritoneal dialysis catheters
erroneously that the antimicrobial fitted with a silver ring which was
action of silver would extend ‘quite gently eased into exit sites allowing
deeply’ into a wound on account of its release of silver ions into the wound
ability to bind albumins and inorganic
anions in the wound site. We now
know that the reverse is true, and that Silastic catheter
silver complexes forming in the wound Silver cuff
bed inhibit penetration (Lansdown
et al, 1997; Lansdown and Williams, Skin
2004). Although metallic silver releases
less that 1ppm Ag+, this is probably
sufficient to control infections in the
acute phase. Nanocrystalline silver
preparations releasing appreciably more Figure 1. Silver nitrate used to treat protruding Figure 2. Silver Cuff Technique to prevent Catheter
ions can be expected to provide more bone fragment. Exit Site Infections.

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 Clinical REVIEW

margin. The technique was effective Silver in surgical procedures a variety of non-metallic suture
in eliminating S. aureus, S. epidermidis Infections encountered at needle and materials coated with a silver ion
and Escherichia coli infections in eight incision sites are potentially the most release compound (such as silver
patients while maintaining germ-free frequent problems arising through zeolite or silver oxide) (Bright et al,
status in 11 of the remaining 12. perforation of the epidermal barrier 2002; Blaker et al, 2004). The first
Groeger et al (1993) conducted a layer (Darouiche, 1999). The presence recorded use of silver sutures derives
similar prospective evaluation using of xenobiotic materials such as suture from gynaecological surgery, when J
silver-impregnated subcutaneous materials, needles, prosthetic devices, Marion Sims (1849) sought to improve
cuffs to prevent ‘tunnelled’ infections external fixation pins and catheters, on his ability to close indolent vaginal
associated with chronic venous greatly enhances the risk of infection; fistulae. In his 30th operation, he
access catheters in 92 patients with and the majority of wound infections successfully used silver wire to close
cancer. Results were less impressive, initiate along and in the vicinity of a major fistula and reported that not
with infections being diagnosed at suture lines (Sugarman and Young, only had the wound healed well but
inser tion sites in seven patients (12 in 1984; Tsai et al, 1987). Most can be that surrounding tissues were not
the control group) with no significant avoided through good hygienic clinical inflamed or subject to overt adverse
difference in infection rates during practice, use of sterile equipment reactions. In 1987 Bashir noted that
the lifetime of the catheters. However, and appropriate postoperative care. daily twisting of silver wire advances
the overall incidence of catheter Whereas it might have been common re-epithelialisation in surgical repair.
tunnel infections in this cohor t of practice a few years ago to use silver
patients was insufficient to allow a surgical knives, silver-coated or silver Darouiche (1999) examined the
valid statistical evaluation. alloy needles, and silver wire sutures antimicrobial efficacy of silver-treated
to control postoperative infections, medical sutures used in surgery and
Bhattacharyya and Bradley (2006) it is rare practice these days, except drew attention to the lack of success
provided an example of how a silver- possibly in ophthalmic surgery (Kloti, in early studies where materials such
release dressing might be used in 1974; Nasr et al, 1983; March et al, as silk, polyethylene terephthalate
the topical management of infections 1987) and in acupuncture (Tanita et al, (Dacron), and catgut, were immersed
due to medical devices, such as 1985; Yi-Kai et al, 2000). in 5% or 50% silver nitrate for
orthopaedic K-wires. These wires, used 24 hours. They failed to inhibit S.
in the external fixation of orthopaedic Acupuncture needles made of aureus infection. Later studies found
fractures, commonly protrude from the silver or gold are used as part of Hari that using a silver-zinc allantoinate
skin with insertion points and tracts therapy for headache, fatigue, back complex was more successful in
providing easy access for opportunist pain etc in oriental medicine (Tanita et controlling staphylococcal infections,
pathogens to vulnerable tissues of al, 1985). Needles consisting of silver possibly on account of the more
the dermis and deeper. Infection rates or gold are implanted intracutaneously sustained release of bactericidal levels
associated with external fixation and possibly left within the skin for of silver ions, and the reduced binding
devices of 21–85% are a cause for several days. Infection does not seem of silver to the suture materials
severe discomfort to patients as well to be a reported problem of needle (Gravens et al, 1973).
as instability of pins and impairment insertion sites in acupuncture but
of their orthopaedic function. excessive release of silver ion is an In one form or another, silver
Bhattacharyya and Bradley (2006) occasional cause of blue macules molecules have been incorporated
treated pin tract infections in 11 of argyria at insertion points and into the surfaces of a large number of
older patients (mean age=66.8 years) elsewhere in the body (Suzuki et medical devices with a view to limiting
with Acticoat-7 dressings (Smith and al, 1993; Takeishi et al, 2002; Kakurai infections. It is unfortunate that as new
Nephew, Hull) and monitored their et al, 2003). Chrysiasis due to technology comes to hand with new
progress over 42 days postoperatively. accumulation of dark complexes of advances in nanotechnology, few have
Although overt signs of infections at gold are occasional complications. been fully evaluated and their real
the external orifice of external fixation Neither condition is of toxicological clinical value appreciated. Cowan et
pins were controlled and wound sites significance but the discolourations are al (2003) refer to the value of silver
healed well following exposure to cosmetically undesirable. zeolite coating for stainless steel and
Acticoat-7 dressing, this treatment was its capacity to reduce colony formation
not superior to that achieved with oral Silver sutures of E. coli, S. aureus and other bacteria
antibiotic therapy. Although details of Metallic sutures have been used by in vitro, but emphasise that the
the nature or severity of the infections surgeons since the times of the early stability of the coating and duration
were not included, the authors Greeks when Galen (130–200 AD) of its antimicrobial action must be
maintained that a topical dressing is reputed to have used ligatures of clarified before the technology can be
such as Acticoat-7 is preferred to oral gold wire (Rucker, 1950). Over the developed for clinical use. Whereas
antibiotics in older patients, for reasons centuries, surgeons have employed significant reductions in ‘colony-
of safety and ease of management. lead, stainless steel, silver wire and forming units’ were reported with five

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 Product REVIEW
Clinical RESEARCH/AUDIT
REVIEW

bacterial strains commonly seen in skin seven strains of wound bacteria in

wounds within four hours of exposure, tissue culture. The responses were
this effect diminished markedly when mixed, whereas P. aeruginosa was most
the coatings had been applied by a sensitive to silver released at anodes,
‘wet process’ and scrubbed between Proteus mirabilis, which presents major
uses. Power-coated surfaces cleansed problems by creeping along encrusting
with a towel offered a higher degree of medical devices, was least sensitive.
antibacterial efficiency.
External fixation pins
A quite different approach to Clayton Parkhill (1897) was possibly
antimicrobial sutures derives from Figure 3. Bioglass Granules observed by Scanning
® the first surgeon to use silver-coated
research in materials science at Imperial Electron Microscopy. devices to fix bone fractures, his
College, London. Following successes steel clamp being heavily coated in
achieved in orthopaedic surgery silver to provide antiseptic action.
with the biodegradable composite Parkhill attempted to create an
Bioglass® (Novabone, Florida) (Figure ‘unfavourable environment’ on the
3) (Wang et al, 1998; Bellantone et al, surface of the fixation devices to
2000; 2002), Blaker et al (2004; 2005) limit bacterial adhesion and this has
engineered a new bioactive suture with also been attempted more recently
antimicrobial properties. Bioglass® is (Shintani, 2004). This concept has been
a family of bioactive glasses that elicit developed widely in the design of
specific physiological responses in orthopaedic pins and screws which are
hard and soft tissues through release commonly colonised by bacterial flora,
of calcium, silicon and phosphate. Figure 4. Mersilk® Fibre doped with silver oxide as notably S. aureus and S. epidermidis
By incorporating silver oxide in this an antimicrobial suture. (Bosetti et al, 2002). Biofilm formation
composite Blaker et al have developed is an additional problem in orthopaedic
an antimicrobial molecule. Using a medicine and fixation devices are
‘slurry dipping’ technique, commercially subject to infections such as P. mirabilis
available resorbable sutures — which adhere to exposed surfaces
polyglactin 910 (Vicryl or the non- and migrate along solid surfaces
resorbable material Mersilk, both from to aggregate and form mineralised
Ethicon, Livingston), were coated with concretions or calyces (Morris et al,
Bioglass® granules to provide new 1997). This results in instability of the
suture material for surgery (Figure 4). devices and can be a cause of severe
Physico-chemical analyses substantiated patient discomfort. Devices including
Figure 5. Dermal macrophage in a rat wound
that this bioactive glass coating did xenobiotic implants and fixation
containing cytoplasmic granules of silver
not significantly influence the tensile devices are not inert but interact with
(x40 objective).
strength or thermal properties of their surrounding environment (Wassall
the suture materials and released et al, 1997; Darouiche, 1999). Bacterial
sufficient silver in a sustained fashion the wound bed as a prerequisite for colonisation may not be immediately
to control S. epidermidis isolates in epidermal regeneration and tissue obvious but can be expected to
vitro (Pratten et al, 2004). The new repair (Lansdown et al, 2003). The increase proportionately with the
suture was effective in limiting bacterial product is without detectable adverse period for which the fixation pins are
attachment and is predicted to have effects and wounds healed normally in place which was shown by Respet et
many applications in wound healing during the study. al (1987) in canine experimentation.
and general surgery. Experimental
studies indicate that the silver Bioglass® Although electrical currents have Pin tract infections may occur in
complex degrades completely in the been used to accentuate silver ion 2–30% of all implants (Green, 1983;
wound bed to release silver, silicon release from silver wire or foil for Massè et al, 2000). Biofilms are made
and calcium ions, each with a defined many years (Spadaro et al, 1974; up of mixed populations of organisms
role in tissue repair (Lansdown et al, Becker, 1986), its application in the use commonly seen in skin wounds; they
1997; Carlisle, 1982; Lansdown, 2002c). of a braided nylon suture impregnated mutate readily and become resistant
Preliminary evaluation of the suture in with a silver compound is of interest to many antibiotics (including silver)
experimental wounds demonstrated (Chu et al, 1987; Tsai et al, 1987). In with colonies providing reservoirs
the central role of dermal macrophages these related studies a silver-containing from which organisms contaminate
in the catabolism of the Bioglass® nylon suture (Nurulon [Ethicon, surrounding tissues as well as
complex and in the metabolism of Livingston]) was connected to a direct systemically (Sheehan et al, 2004).
silver (Figure 5), calcium and silicon in electric current and shown to inhibit Resistance plasmids between different

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 Clinical REVIEW

bacterial strains are readily exchanged coating was effective in reducing the (Meyer et al, 2004). In a sheep model,
by conjugation. Problems associated incidence of E. coli, P. aeruginosa and stainless steel, titanium, colloidal silver-
with biofilm formation in the use S. aureus on orthopaedic pins in vitro, coated and stainless steel pins coated
of orthopaedic devices, catheters it actually enhanced the adhesion of in a polyurethane-argentum sleeve
for intravascular, intraperitoneal or Staphylococcus haemolyticus (Wassall were evaluated. Although there was a
suprapubic insertion, orthopaedic et al, 1997). Further, when 36 silver- trend towards lower infection rates for
prostheses and bone cements and coated and 12 uncoated stainless S. aureus infection for the silver-treated
other medical devices are fully steel pins were implanted into the pins, the effect was not significantly
discussed elsewhere (Donlan, 2002; iliac crest of six sheep and inoculated different from other pin types.
Dunne, 2002). Whereas early studies with S. aureus, 84% of the uncoated Although colloidal silver exhibited
indicated that silver coating was pins were infected while only 62% of no appreciable influence on pin tract
an efficacious means of controlling the silver-coated pins were infected infections, it was reported to show
bacterial adhesion and colony as shown by electron microscopy improved results regarding osteolysis
formation associated with pins and (Collinge et al, 1994). This difference caused by S. aureus infection.
devices for fixation of bone fractures, is not statistically significant but silver-
this has not been substantiated coated pins were loose less frequently Coating orthopaedic implants with
in experimental or clinical studies than uncoated pins and pin motion an antimicrobial layer of titanium/
(Darouiche, 1999). was closely correlated with infection. silver (2µm thick) via a physical
Not unexpectedly, when silver-coated vapour deposition process in an inert
The hypothesis that silver coating fixation pins were pre-conditioned by atmosphere of argon was evaluated
will decrease bacterial colonisation and exposure to human serum, bacterial recently for antibacterial efficacy
pin tract infections has led to a range adhesion was in most cases significantly (Ewald et al, 2006). Although titanium
of technologies and experimental greater than in unconditioned pins. has no recognised antibacterial effect,
studies in rabbits and sheep. In early Albumins and macroglobulins in the this coating released 0.5 to 2.3ppb
studies, Colmano et al (1979; 1980) serum reduced the efficacy of the silver when immersed in saline and
implanted intramedullary silver- silver by binding free ions (Wassall exhibited significant antimicrobial
electroplated pins in rabbit femurs et al, 1997). Similarly unconvincing potency against S. aureus and Klebsiella.
and applied a direct electric current. observations were made in an sp. As in previous studies (Bosetti et
Stainless steel pins coated with experimental study where silver-coated al, 2002), the silver-coating technology
100 monomolecular layers of silver K-wires were inserted into rabbit was without adverse effects on
stearate resulted in a 69% reduction femurs to mimic conditions of human osteoblasts and epithelial cells in
of S. aureus within one hour. These orthopaedic surgery (Sheehan et al, culture. Clinical evaluation is awaited.
observations compared favourably 2004). This study further confirmed
with later work in which stainless steel the limited capacity of silver to control Safety in use
pins were coated with silver (2.5%) biofilm formation, at least with S. aureus Use of silver metal, silver impregnation
and zinc (14%) zeolite (Bright et and S. epidermidis. or silver coating in medical devices for
al, 2002) without use of an electric implantation, pin tracts or exit sites
current (Cowan et al 2003). Clinical evaluation of SPI-Argent in the body wall has not generally
treated external fixation pins/screws given rise to concern about toxicology.
The SPI-Argent technology (Spire in the management of limb fractures Allergy and delayed hypersensitivity
Biomedical, Bedford, Mass) has been in 24 male patients demonstrated a to silver have not been recorded and
subject to more comprehensive reduction in pin tract infections, but confirmed reactions to silver in regions
investigation (Collinge et al, 1994; the observations were not significantly local to implants or elsewhere in the
Wassall et al, 1997; Massè et al, 2000). different from those seen in patients body are rare. Limited subjective
Silver coating of orthopaedic fixation treated with commercially available observations suggest that silver acts
pins and screws was achieved by stainless steel devices (Massè et al, as an anti-inflammatory agent. Wound
exposing stainless steel to an ion- 2000). S. aureus was most frequently sites have been reported to heal well
beam assisted deposition of silver cultured from screw tips. Ethical following removal of silver-coated
granules (50–150nm diameter) from considerations and a lack of statistically devices with no obvious sequelae
a vapour phase. The technology significant observations resulted in (Massè et al, 2000). Darouiche (1999)
enabled deposition of an homogenous a discontinuation of the work. No did add the caveat that it is prudent to
coating of silver on the surface of adverse effects were seen in or near ensure that, while constructing silver-
stainless steel. Distribution patterns implantation sites, including overt signs coated medical prostheses or other
have been monitored using scanning of infection. devices, silver is incorporated onto
electron-microscopy and energy the surfaces at concentrations that are
dispersive X-ray analysis (EDAX) Colloidal silver has been used to adequate for the reduction of bacterial
(Wassall et al, 1997). Preliminary coat external fixation pins in an effort adhesion but not high enough to evoke
studies showed that while the silver to remove risks of pin tract infections systemic toxicity.

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Release of silver ions from the Reduced antimicrobial action of the amount of silver actually ‘available’
various devices discussed has been silver-containing dressings or silvered over and above that bound in stable
quantified using energy dispersive X- medical devices is attributable to three complexes with inorganic anions,
ray spectrometry but rarely have silver main causes: albumins and macroglobulins in wound
levels in the blood been measured. 8 Silver-resistant organisms (including exudates and secretions, and to living
Massè et al (2000) in their clinical biofilm formation) tissues of the host.
evaluation of fixation pins coated by 8 Insufficient ‘available’ silver ion in
the SPI-Argent method, reported a the medium, wound bed, pin or Nanocrystalline silver as the
rise in blood silver from 0.2µg/l to a needle tract to exert a lethal action bioactive principle of Acticoat® (Smith
medial level of 2.79µg/l after seven on sensitive strains & Nephew, Hull) and some antibiotic
days and 3.2µg/l after two months. 8 Epigenic mechanisms. coatings for medical devices releases
Although this rise is statistically 70–100µg Ag+/ml in the presence of
significant, it is substantially below Although skin wounds, orthopaedic moisture and wound fluids, whereas
threshold limit values set by the fixation pin implantation sites, metallic silver (foil, coating, wire)
Food and Drug Administration of PEG drainage and even suturing possibly releases less than 1µg/ml
the USA and the 14µg/l reported may provide a sufficiently stressful (Burrell, 2003; 2004). Data is not
as an acceptable non-toxic value environment to select for antibiotic available for silver zeolite or colloidal
for precious metals derived from a resistance (Gupta et al 1999), there silver as used in some coatings. Clearly,
literature search (Perrelli and Piolatto, is no tangible evidence so far to the relative inefficiency of the silver
1992). show that it actually occurs. Silver- or silver coating in reducing bacterial
resistant bacteria have been identified adhesion and device-related infections
Discussion in patients with burn wounds, water must be attributable to the fact that in
Silver is a well recognised antimicrobial effluents and photographic sludges, pin, needle and device tracts, silver ion
agent with a broad spectrum of action but available information indicates that binding to host tissues and exudates
against opportunist pathogens infecting it is a rare event (Russell and Hugo, outweighs the amount available for
wound sites. While numerous clinical 1994; Percival et al, 2005). There is antimicrobial action. Even in tissue
trials have demonstrated the ability of no substantive evidence to show that culture, silver ion is readily bound
the various sustained silver ion release prolonged exposure to silver in any to chloride ion, nutrients in the agar
dressings to control microbial flora in clinical situation predisposes to silver medium and electrolytes. This means
acute and chronic wounds, a limited resistance. that as in preliminary studies by the
experience, discussed above, points author, a concentration of silver nitrate
to their capacity to limit infections at Preliminary studies in the author’s of 1.0mM necessary to kill most wound
sites of insertion (and exit) of medical laboratory have shown that all but one bacteria in a wound is not a true
devices including orthopaedic fixation bacterium isolated from chronic ulcer reflection on the silver concentration
pins and gastronomy devices which patients is sensitive to silver (1.0mM to be obtained in a wound bed for
protrude from the skin for several days AgNO3) in plate culture; a strain of total bactericidal action.
or weeks. Enterobacter cloacae was found to
grow in the presence of 1.0mM AgNO3 Epigenic (non-genetic) mechanisms
Experience has shown that and revealed molecular evidence of of microbial resistance to silver or other
although silver, silver nitrate and genetical resistance to silver (Lansdown metal cations are not well defined.
dressings that release silver ion et al 2004a; 2005). This suggests that Studies by Gupta et al (1999) have
do control wound flora and aid, the large proportion of bacteria in a demonstrated that the action of silver
and thereby advance wound bed wound site exposed to metallic silver, on sensitive bacteria and fungi is largely
preparation, they rarely lead to a silver coatings or silver ion releasing attributable to a genetically-mediated
germ-free wound site. Also there is dressings should be killed. uptake of lethal concentrations of ionic
often poor agreement between in silver. However, they also report that
vitro trials that test for antimicrobial Burrell et al (2004) estimated halide ions in the medium can influence
action against named pathogens that silver ion should be available the expression of natural sensitivity or
(usually bacteria) and clinical at concentrations of 10–40ppm to resistance to silver (Gupta et al, 1998).
experience. This situation is true both kill most organisms and 60ppm to Low concentrations of silver increased
in the case of dressings designed for eliminate the most resistant strains the minimal inhibitory concentration
chronic skin wounds and ulcers, and including methicillin-resistant S. aureus. between sensitive and resistant
in the preparation of medical devices Although wide variations exist in the strains, high levels of halide increased
including catheters, intraperitoneal actual amount of silver released by the the sensitivities of both strains. The
drainage devices, wound sutures and various wound dressings and silver- extent to which this or other epigenic
external fixation pins/screws treated treated medical devices, it is important mechanisms contribute to reduced
with silver metal or other ionisable to recognise that the antimicrobial antimicrobial efficacy in in-dwelling
silver compound. effect can only be measured in terms of medical devices is not known.

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silver resistance in bacteria and the Carlisle EM (1982) The nutritional

Key Points relative inactivity of silver on biofilm essentiality of silicon. Nutr Rev 40(7):
193–8
formation. WUK
Chu CC, Tsai WC, Yao JY, Chiu SS (1987)
8 Silver is an efficacious anti- I am grateful to Patrick O’Sullivan of the Newly made antibacterial braded nylon
Pharmacy Clinical Information at Charing Cross sutures. I. In vitro quantitative and in
microbiological agent which Hospital for his diligent enquiries into the use of
silver and silver-coated devices in clinical medicine vivo preliminary biocompatibility study. J
ionises in the presence of Biomed Mater Res 21(11): 1281–1300
in the UK.
moisture or wound fluids to kill
genetically-sensitive organisms. Collinge CA, Goll G, Seligson D, Easley
KJ (1994) Pin tract infections: silver vs
uncoated pins. Orthopedics 17(5): 445–8
8 Silver ions released from References
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medical dressings and Bashir AH (1987) Wound closure by (1979) Activated silver coatings for
surgical devices are effective skin traction: an application of tissue surgical implants. Va Med 106(12): 928–30
in controlling infections and expansion. Br J Plast Surg 40(6): 582–7
Colmano G, Edwards SS, Barraanco SD
improving the clinical use of Becker RO (1986) Silver in Medicine. (1980) Activation of antibacterial silver
orthopaedic fixation pins, Precious Metals. Proc Int Precious Met Inst coatings on surgical implants by direct
catheters and devices inserted Conf (9th Edn). Zysk JA Bonnuci, Pub Int electrical current: preliminary study in
percutaneously. Precious Met Inst. Allentown Pa: 351–7 rabbits. Am J Vet Res 41(6): 964–6
Bellantone M, Coleman NJ, Hench LL Cowan MM, Abshire KZ, Houk SL, Evans
8 New technology has led to (2000) Bacteriostatic action of a novel SM (2003) Antimicrobial efficacy of a
development of silver-coated four-component bioactive glass. J Biomed silver-zeolite matrix coating on stainless
or silver-containing sutures, in- Mater Sci 51: 484–90 steel. J Ind Microbiol Biotechnol 30(2):
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