The effect of silicone sheeting on the production of exoproteins by microorganisms

Hypertrophic scarring is common amongst burn injuries. Pressure therapy and the use of silicone sheeting is often prescribed to treat these scars, but there is weak evidence of the effect of silicone sheeting during treatment. At present, it is not known how the silicone dressings work. In this setting, it has been proposed that water transmission may play a role. The treatments provide favourable conditions for bacteria to colonize and multiply due to the sheeting being worn for at least 12 hours at a time and there are no studies investigating the microorganisms found on fully healed wounds before or after treatment with silicone. As it is unclear on how effective silicone sheeting may be in treating hypertrophic scars, there could be an efficiency factor due to microorganisms found under the dressings. This study aimed to investigate the microbiology of intact skin under silicone sheeting and to construct a model to study the in-vitro effects on extracellular protease production. In-vitro models were set up to determine bacterial numbers and protease activity. Various models were constructed using Petri dishes and universals with broth to allow organisms to permeate throughout the silicone dressings. An azocasein substrate was used to quantify total protease levels. Ten healthy volunteers were recruited into the study and one volunteer presented with considerable hypertrophic scarring and agreed to be a case study. Swabs were taken of the skin prior to application of silicone sheeting, and then the skin and sheeting were swabbed subsequently once a week over a one-month period. In-vitro results showed increases in bacterial growth for all organisms tested, but protease activity increase was only displayed by S.epidermidis, S.aureus, A.johnsonii and C.albicans. A.johnsonii showed a significant change in protease activity (P=0.020) as well as S.aureus (P=0.001). The volunteer study revealed variable results, which may have been due to interference with the azocasein assay. An ANOVA showed no statistical significance. The mechanism of action of silicone treatment remains inconclusive and requires further study