In vitro Study of the Efficacy of a Novel Antimicrobial Dressing with Soft Silicone Adhesive in a Diffusion Model Mimicking a Catheter Insertion Site

Objective:

This poster describes the results of a study that was undertaken to assess the in vitro efficacy of an antimicrobial dressing with soft silicone adhesive*, against bacterial growth under a catheter covered by the dressing.

Methods:

To mimic an insertion site, pieces of intravenous catheters were placed on blood agar plates containing simulated wound fluid. Circular dressing pieces  were applied on top of the catheter. The assemblies were then incubated at 35°C ±2°C for 24 hours. For comparison the same test was performed using Mueller Hinton agar. On the following day, the dressing and catheter were removed and Staphylococcus epidermidis (ATCC 14990, 1.5-3.0 X 10⁶ CFU/ml) was spread over the plate and incubated for an additional 24 hours at 35°C. The plates were photo-documented and the diameter of the zone of inhibition was measured.

Results:

No bacterial growth was detected under the catheter and clear zone of growth inhibition was observed on both blood agar and Mueller Hinton agar. The diameters of the clear zones were markedly reduced on the blood agar compared to Mueller Hinton agar. The antimicrobial dressing with soft silicone adhesive was found to inhibit bacterial growth. The zones were clearly smaller on blood agar than Mueller Hinton agar plates, indicating that the choice of medium can influence the results of the antimicrobial testing. It is believed that the blood agar plates with added serum proteins more closely resemble the environment of an actual intravascular insertion site.

Conclusion:

The study demonstrates that the antimicrobial dressing with soft silicone adhesive has the ability to prevent bacterial growth on the surface and also under the catheter covered by the dressing (i.e. even where the dressing is not in direct contact with the surface).