Evaluation of the efficacy of an iodine based wound dressing against biofilms using confocal scanning laser microscopy when in direct contact and when in an artificial wound eschar model

Biofilms form when bacterial cells aggregate with each other and on surfaces and secrete extracellular polymeric substances, encasing the cells in a matrix. Biofilms can form when wounds become infected, leading to delayed wound healing and the formation of chronic wounds.

The aim of this study was to investigate the efficacy of an iodine based wound dressing against biofilm when in direct contact with a biofilm and in the presence of artificial wound eschar (AWE) to better represent a wound environment, using confocal scanning laser microscopy (CLSM). To grow the biofilms LabTek chamberslides were inoculated with overnight cultures of Pseudomonas aeruginosa and Staphylococcus aureus adjusted to 1 x 106 CFU/mL. Chamberslides were incubated at 37°C and 125 rpm for 24 hours. To assess direct contact with the biofilm, dressings were added directly to the chambers ensuring contact with the biofilm.

For the AWE model, AWE (65% collagen, 10% elastin and 25% fibrinogen and converted by thrombin) was added on top of the biofilms before adding the dressings to the chambers. Dressings were hydrated with SDW and chamberslides were incubated for 30 minutes and 24 hours, before staining of the biofilms with LIVE/DEAD™ Baclight™ fluorescent stains (SYTO 9® and propidium iodide). Stained biofilms were visualised with an LSM 780 Zeiss confocal microscope with a 40x (0.9 NA) air objective. The results demonstrated that the iodine based dressing is efficacious against 24 hour P. aeruginosa and S. aureus biofilms after an exposure time of only 30 minutes and that it can penetrate the artificial eschar and slough to exert its antibiofilm effect.

The iodine based wound dressing demonstrated a higher penetration ability through the AWE in comparison to the other dressings tested. The data shows that the iodine based dressing effectively manages biofilm in vitro. Clinical significance cannot be determined.