Silver Dressings for Wound Treatment

The presentation by one of the United Kingdom’s leading wound care specialists, Dr. Daniel Metcalf, at the Wound Treatment Association conference attracted considerable interest. He discussed the possibilities, indications, and advantages of using a new generation of silver dressings in the treatment of infected wounds, particularly their beneficial effect on biofilm formed by pathogens on the wound surface. Dr. Ingrida Ašakienė’s presentation also drew the audience’s attention because it introduced a clinical algorithm for assessing and identifying wound biofilm. Biofilm formation in wounds creates favorable conditions for microorganisms to multiply rapidly and delays wound healing.

Today, wound infection is understood as the host organism’s response to pathogens. The local response manifests as an inflammatory reaction, including tissue redness, swelling, pain, increased temperature, and an unpleasant odor. The patient’s immune cells, particularly neutrophils, attack pathogenic microorganisms by releasing tissue-degrading enzymes such as lysozymes and myeloperoxidases. Pathogens produce exotoxins, while the death of microorganisms releases endotoxins contained within them. The presence of microorganisms in a wound does not necessarily indicate infection. Infection is a process of interaction between the microorganism and the host organism. It develops through several stages: wound contamination, colonization, critical colonization, and infection.

Some microorganisms are more likely than others to cause wound infection, including methicillin-resistant Staphylococcus aureus, beta-hemolytic streptococci, certain fungi, and aerobic and anaerobic pathogens. According to Dr. D. Metcalf, recent studies have shown that other factors are also crucial in the development and progression of wound infection and may significantly impair the healing process. These include excessive exudate and, particularly, biofilm. Pathogenic cells can adhere to various surfaces, both viable, such as the wound bed and tissues, and non-viable, such as sutures and dressings. There, pathogens become embedded in an extracellular polymeric matrix, in effect hiding within it and becoming resistant or less sensitive to the patient’s immune cells and antimicrobial agents, including antibiotics and antiseptics.

Biofilm – bacterial colonies producing polysaccharide “armor”

In her presentation, Dr. Ingrida Ašakienė emphasized that biofilm is an active biological structure consisting of communities of microorganisms functioning within an extracellular matrix. Biofilm is a common form of microbial existence: approximately 80% of infections are associated with biofilm formation. Dental plaque, urinary tract infections, and eye infections are also frequently related to biofilm. Approximately 60% of chronic wounds are covered with biofilm. Microorganisms form biofilms in order to multiply more rapidly.

Biofilms weaken the body’s immune response. Microorganisms within biofilms form metabolic consortia: one microorganism becomes a food source for another, primitive exchange of genetic information takes place, and resistance to phagocytosis and antibiotics is promoted.

Microorganisms within biofilms often exhibit high pathogenicity. Unlike individual bacteria, biofilms are more resistant to antibiotics. Pathogens may remain viable within biofilms even at antibiotic concentrations 1,000 times higher than the usual therapeutic dose. Antibacterial agents have difficulty penetrating the polysaccharide layer of the biofilm, which acts as a biological adhesive, firmly attaching the biofilm to the bacterial cell surface.

Biofilm forms a mechanical barrier to epithelialization, weakens the cellular immune response, maintains the inflammatory phase of the wound, and promotes the transition from an acute wound to a chronic wound.

It has been established that the presence of biofilm increases the risk of infection. Biofilm is one of the most important factors delaying wound healing. At least 60% of chronic wounds are covered with biofilm. Biofilm frequently forms in chronic wounds, surgical wounds, and fistulas. It is not destroyed by antiseptics such as PHMB, honey, iodine solutions, or silver, by antibiotics, or by the body’s own attempts to cleanse and heal the wound. Biofilm impairs wound healing by suppressing the local immune response, inhibiting epithelial cell migration, and preventing the formation of granulation tissue. Some pathogens form more dangerous biofilms. Polymicrobial biofilms formed by multiple microorganisms are more hazardous because they delay wound healing more effectively than single-species biofilms. Poor wound healing prolongs treatment, reduces the patient’s quality of life, and increases treatment costs. Biofilm can be identified by examining the wound:

▪ the wound is covered with a matte or glossy mucus-like substance resembling milk;

▪ the film is pale green or yellow because of pigment;

▪ it can be removed relatively easily by gentle scraping;

▪ the removed film rapidly reforms;

▪ it is poorly responsive to antibacterial agents.

Therefore, in clinical practice, it is very important to assess and predict when a chronic wound may become complicated by biofilm formation and to determine the appropriate subsequent treatment algorithm for a wound covered with biofilm.

At least 60% of chronic wounds are covered with biofilm. It has been established that biofilm formation increases the risk of wound infection and is the most important factor delaying wound healing. Biofilm delays healing by suppressing the local immune response, inhibiting epithelial cell migration, and preventing granulation tissue formation.

Dr. Ingrida Ašakienė

Aquacel Ag + Extra dressing was specifically developed for the treatment of wounds covered with biofilm and for more effective management of wound infection. The combination of Hydrofiber and Ag + technologies provides the strongest effect against wound infection: it disrupts the biofilm, destroys bacteria, and prevents biofilm from reforming.

Dr. Daniel Metcalf

Possibilities of Modern Treatment of Infected Wounds

Until 1996, the only treatment options for exuding wounds were cotton dressings or cold compresses. In 1996, the pharmaceutical company ConvaTec introduced a new generation of hydrocolloid Aquacel Hydrofiber dressings. In 2002, antimicrobial silver dressings, Aquacel Ag, began to be used in clinical practice, and in 2014 the most advanced care and treatment option for infected wounds or wounds at risk of infection was introduced: Aquacel Ag + Extra dressings. All dressings in the Aquacel Ag family, including Aquacel Ag Foam and Aquacel Ag + Extra, have a broad spectrum of antimicrobial activity. They act against aerobic and anaerobic bacteria, Candida fungi, and methicillin-resistant and vancomycin-resistant pathogens. Silver destroys most common pathogens responsible for wound infection. Silver and other antiseptics incorporated into dressings actively combat wound pathogens by:

▪ disrupting the microbial cell wall;

▪ inhibiting DNA synthesis;

▪ denaturing proteins and enzymes;

▪ blocking protein synthesis in ribosomes.

Standard antiseptic dressings are effective only when adequate penetration of the antiseptic into the wound is ensured and the wound is not covered with biofilm. Comparative studies have shown that not all antiseptics and antibiotics used in clinical practice effectively penetrate wound biofilm. Most standard antimicrobial substances are simply ineffective against biofilm. Biofilm cannot be eliminated using standard antimicrobial dressings. Increasing the amount of antimicrobial substance compromises the safety and physical properties of the dressing, including absorption and contact with the wound.

Special biofilm-disrupting substances may be used to break down the biofilm and make the bacteria hidden within it more susceptible to antibiotics.

Aquacel Ag + Extra was specifically designed to combat biofilm and wound infection, making it a new and highly effective antimicrobial dressing. Aquacel Ag + Extra is manufactured using Hydrofiber and Ag + technologies, which provide the strongest effect against biofilm and enable effective treatment of wound infection.

The combination of these two technologies, Hydrofiber and Ag +:

▪ promotes faster diffusion of biofilm into the dressing’s gel layer;

▪ protects silver ions from competing reactions;

▪ increases Ag + diffusion through the bacterial cell wall and biofilm;

▪ disrupts and helps remove biofilm;

▪ makes bacteria within the biofilm susceptible to silver ions, antiseptics, and antibiotics.

Aquacel Ag + Extra dressings:

▪ absorb and “lock in” wound exudate;

▪ maintain a moist wound-healing environment;

▪ disrupt biofilm;

▪ eliminate bacteria;

▪ prevent biofilm from reforming;

▪ protect the surrounding skin from maceration.

Owing to Hydrofiber technology, Aquacel Ag + Extra absorbs wound exudate and locks it into the dressing, forming a gel layer. This creates an optimal moist environment for wound healing, allows the dressing to conform closely to the wound bed, maintains the appropriate moisture level, reduces the risk of pathogen transmission and maceration, and prevents the accumulation of exudate and bacteria and the formation of biofilm.

Aquacel Ag + Extra is distinguished by its exceptionally high absorption capacity and mechanical strength. It can therefore absorb and retain a large amount of exudate without disintegrating when removed from the wound. Removal of the Aquacel Ag + Extra dressing does not traumatize the tissues, and the patient does not experience pain during dressing changes. These dressings may remain on the wound for several days, but no longer than seven days.

Ag + technology is a unique silver formulation with bactericidal activity. It contains components that disrupt biofilm, dissolve the mucus-like substances forming the biofilm, and allow silver ions to penetrate toward the bacteria.

Some free silver ions are inactivated by the polysaccharides within the biofilm. However, the chelating agent EDTA incorporated into the dressing protects the silver ions from these polysaccharides, while benzalkonium chloride reduces biofilm adhesion and facilitates the penetration of silver ions toward wound pathogens. Ag + technology therefore protects silver ions from biofilm polysaccharides and increases the antimicrobial efficacy of the silver dressing. Aquacel Ag + Extra is currently one of the most effective antimicrobial dressings and acts comprehensively by maintaining a moist wound-healing environment, eliminating biofilm, and preventing its reformation.

This hydrocolloid dressing has been reimbursed in Lithuania for non-healing ulcers, wounds, and pressure ulcers lasting more than 30 days. It may also be used for burns and is reimbursed for the treatment of burns in children under 18 years of age.

Prepared on the basis of the presentations “The Effect of Silver on Wound Infection and Biofilm: Comparison With Other Antimicrobial Preparations” by Dr. D. Metcalf, United Kingdom, and “Clinical Algorithm for Identifying Wound Biofilm” by Dr. I. Ašakienė.

Source: “Lithuanian Doctor’s Journal”