Antimicrobial Activity of Silver-Containing Dressings is Influenced by Dressing Conformability with a Wound Surface
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The SCH dressing is made of the hydrocolloid polymer carboxymethylcellulose to which silver ions are attached.14 The dressing fibers absorb wound fluid, swelling to form a soft cohesive gel that covers the wound surface.15 This moist gel mass is kept in direct contact with the wound bed leaving little or no space between the dressing and the wound.16 The ionic silver in the dressing has been shown to provide broad-spectrum antimicrobial activity for up to 14 days.11
In contrast, the NSC dressing consists of 1 layer of a rayon/polyester inner core sandwiched between 2 layers of polyethylene net.17 This net is coated with nanocrystalline silver that is released when water contacts the dressing.18 Studies have shown that silver release from NSC dressings is faster and is delivered more rapidly than from either silver nitrate or silver sulfadiazine dressings.19 The NSC dressing provides an effective antimicrobial barrier for up to 7 days.17
This study used in-vitro models to assess the conformability of SCH and NSC dressings to unevenly contoured wound-like surfaces and to examine the degree to which this correlated with antimicrobial effect against 2 common wound pathogens, Pseudomonas aeruginosa and methicillin-resistant Staphylococcus aureus.
Dressing contact with wound tissue and simulated dry eschar. Small sections of wound tissue obtained from electively amputated lower limbs and simulated dry eschar (human dermis, approximately 10 mm x 4 mm, dried overnight at 37oC) were fixed in a vertical plane on a freshly cleaned microscope slide using a cyanoacrylate adhesive (LOCTITE® 4062 instant adhesive, Loctite, Hertfordshire, UK). The Ethics Committee of North East Wales Trust, Wrexham Maelor Hospital, UK, granted ethical approval to allow human skin to be used from lower limb amputations.
A dry piece of each silver-containing dressing (approximately 10 mm x 4 mm) was then placed carefully onto the upper tissue surface. Glass inserts were placed at either end of the microscope slide to allow a second slide to be placed on top of the tissue and dressing to create a sandwich effect. The ends of the combined microscope slides were then clamped together using bulldog clips, allowing the slide to be placed horizontally onto a microscope stage (Wild Heerbrug, Germany). Images were captured using an attached digital camera (Polaroid DCM 1e, Polaroid Corporation, Waltham, Mass, USA).
Once the dry images had been captured, water was added to each dressing to ensure hydration to saturation point without causing a visible fluid leakage. The volumes used were up to a maximum of 100 µL for the NSC dressing and up to 400 µL for the SCH dressing. Water was added through the gap between the slides to allow observation of the dressing/tissue interaction in the hydrated state.
Dressing contact with an inoculated indented agar surface. Standard reference strains of methicillin-resistant Staphylococcus aureus (MRSA) (NCTC 12232) and antibiotic-resistant Pseudomonas aeruginosa (NCTC 8506) were used to investigate the effect of dressing conformability on antimicrobial efficacy for a SCH dressing and a NSC dressing.
An agar plate model was developed to investigate dressing conformability, ie, the degree to which each dressing maintained intimate contact with a surface-inoculated agar plate during a specified time period. Nonwoven, fabric-folded 4 cm x 4 cm swabs (Topper 8, Johnson & Johnson, Somerville, NJ, USA) were aseptically transferred to the center of standard, pre-dried tryptone soy agar plates (TSA, Lab M) and pressed onto the agar to enable direct contact without damage to the agar surface. A 15-mL volume of molten TSA (precooled to approximately 40oC) was then poured over each swab-impregnated plate to create a second 2–3 mm layer of agar.
1. Bowler PG, Duerden BI, Armstrong DG. Wound microbiology and associated approaches to wound management. Clin Microbiol Rev. 2001;14(2):244–269.
2. Sibbald RG, Williamson D, Orsted HL, et al. Preparing the wound bed—debridement, bacterial balance, and moisture balance. Ostomy Wound Manage. 2000;46(11):14–35.
3. Bowler PG. Progression toward healing: wound infection and the role of an advanced silver-containing Hydrofiber dressing. Ostomy Wound Manage. 2003;49(Suppl 8A):2–5.
4. Wright JB, Lam K, Burrell RE. Wound management in an era of increasing bacterial antibiotic resistance: a role for topical silver treatment. Am J Infect Control. 1998;26(6):572–577.
5. White RJ, Cooper R, Kingsley A. Wound colonization and infection: the role of topical antimicrobials. Br J Nurs. 2001;10(9):563–578.
6. Ovington LG. The truth about silver. Ostomy Wound Manage. 2004;50(9A Suppl):1S–10S.
7. Campton-Johnston S, Wilson J. Infected wound management: advanced technologies, moisture-retentive dressings, and die-hard methods. Crit Care Nurs Q. 2001;24(2):64–77.
8. Percival SL, Bowler PG, Russell D. Bacterial resistance to silver in wound care. J Hosp Infect. 2005;60(1):1–7.
9. Parsons D, Bowler P, Myles V, Jones S. Silver antimicrobial dressings in wound management: a comparison of antibacterial, physical, and chemical characteristics. WOUNDS. 2005;17(8):222–232.
10. Tachi M, Hirabayashi S, Yonehara Y, Suzuki Y, Bowler P. Comparison of bacteria-retaining ability of absorbent wound dressings. Int Wound J. 2004;1(3):177–181.
11. Bowler PG, Jones SA, Walker M, Parsons D. Microbicidal properties of a silver-containing hydrofiber dressing against a variety of burn wound pathogens. J Burn Care Rehabil. 2004;25(2):192–196.
12. Jones SA, Bowler PG, Walker M, Parsons D. Controlling wound bioburden with a novel silver-containing Hydrofiber dressing. Wound Repair Regen. 2004;12(3):288–294.
13. Gallant-Behm CL, Yin HQ, Liu S, et al. Comparison of in vitro disc diffusion and time kill-kinetic assays for the evaluation of antimicrobial wound dressing efficacy. Wound Repair Regen. 2005;13(4):412–421.
14. AQUACEL Ag [package insert]. Skillman, NJ: ConvaTec; 2002.
15. Bowler PG, Jones SA, Davies BJ, Coyle E. Infection control properties of some wound dressings. J Wound Care. 1999;8(10):499–502.
16. Robinson BJ. The use of a hydrofibre dressing in wound management. J Wound Care. 2000;9(1):32–34.
17. Acticoat [package insert]. Hull, UK: Smith & Nephew; 2002.
18. Demling RH, DeSanti L. The role of silver in wound healing. Part 1: effects of silver on wound management. WOUNDS. 2001;13(1 Suppl A):5–14.
19. Yin HQ, Langford R, Burrell RE. Comparative evaluation of the antimicrobial activity of ACTICOAT antimicrobial barrier dressing. J Burn Care Rehabil. 1999;20(3):195–200.