IN-VITRO ASSESSMENT OF WOUND DRESSING BACTERIAL SEQUESTRATION Lovett J., Roberts S., Stephenson C.

Introduction: The increased length of time without the skin’s protective barrier in a chronic wound leaves them naturally susceptible to bacterial infection. Bacterial colonisation in a wound has been linked to delayed healing therefore it is desirable to keep bacteria in wound fluid away from the wound surface. Dressings for chronic wounds are designed to absorb excess wound fluid, therefore have the potential to take up bacteria present within this fluid. This test has been designed to understand the ability of a range of foam dressings to keep bacteria away from the wound surface following absorption and retention on compression. Aim: To test a selection of foam dressings (A,B,C,D*) for their ability to sequester bacteria through absorption and retention on compression. *Brand names- Dressing A- KerraFoam Gentle Border (Crawford Healthcare); Dressing B-Allevyn Gentle Border (Smith & Nephew); Dressing C-Aquacel Foam (Convatec); Dressing D- Mepilex Border (Mӧlnlycke Healthcare)

Diluted bacterial solution Method: A single colony of Pseudomonas Aeruginosa was cultured overnight at 37 o C. The culture was diluted 1: ul of the diluted culture was plated out for Total Viable Counts (TVC) and incubated overnight at 37 o C. 35ml of the overnight culture was then poured onto each dressing. The dressings were left until all of the fluid had been absorbed, and then for a further two minutes to ensure that the fluid was within the dressing as opposed to on the surface. The dressings were compressed by hand until no further fluid was able to be released. The released fluid from each dressing was then weighed, serial diluted and plated out for incubation overnight at 37 o C. TVC was then conducted on each plate. Triplicate 100 µl Triplicate Mueller-Hinton Agar plates 100 µl dressing Serial dilutions dressing 2 minutes 35ml

Results: Sample Average Fluid released upon compression % fluid released% fluid retained Initial bacterial solution added to dressing 35mlN/A A0.09g B23.98g C15.21g D23.83g *Brand names- Dressing A- KerraFoam Gentle Border (Crawford Healthcare); Dressing B-Allevyn Gentle Border (Smith & Nephew); Dressing C-Aquacel Foam (Convatec); Dressing D- Mepilex Border (Mӧlnlycke Healthcare) Dressing A was shown to retain the largest quantity of the absorbed fluid, keeping 99.74% of the bacterial solution within the dressing structure. Dressings B and D were able to retain the least amount of fluid, releasing approximately 69% upon compression. It was hypothesised that an increased volume of fluid released from a dressing would release a higher quantity of bacteria into a wound, however it was possible that the dressings would retain the bacteria, but elute the fluid, therefore decreasing the concentration of bacteria present. The collected fluid was therefore serial diluted and plated out in order to establish the quantity of bacteria re-released upon compression.

Conclusion: Of the dressings tested Dressing A was shown to have the highest capability for retaining solutions containing bacteria, releasing the smallest quantity of bacteria upon compression. *Brand names- Dressing A- KerraFoam Gentle Border (Crawford Healthcare); Dressing B-Allevyn Gentle Border (Smith & Nephew); Dressing C-Aquacel Foam (Convatec); Dressing D- Mepilex Border (Mӧlnlycke Healthcare)