Biofilm Inactivation with the Use of an Iodine Based Wound Dressing

Wounds readily colonised by microorganisms often develop biofilms; a community of resilient microbes which can cause increased inflammation and delay the healing process.

Biofilms are inherently more tolerant to antimicrobials compared with their planktonic counterparts making them a challenge to eradicate. To combat this, in both acute and chronic infections, wound dressings employ antibacterial agents for their broad mechanism of action and reduced likelihood of resistance.

In recent years, iodine-based antimicrobials have been shown to promote the wound healing process whilst eliciting antibacterial activity against key Gram positive and negative bacteria. In this study, we assessed the antibiofilm activity of an iodine-based foam dressing with two comparator dressings, silver-based carboxymethylcellulose and methylene blue and gentian violet polyvinyl alcohol foam, against methicillin-resistance Staphylococcus aureus (MRSA), Pseudomonas aeruginosa and vancomycin-resistant Enterococcus faecalis (VRE) biofilms.

The biofilms were generated using a CDC bioreactor model, in accordance with ASTM E2871-13, and a chamber slide model at 37 ˚C under shear for up to 72 hours before being exposed to each treatment. The antibiofilm activity of the dressings was determined by culture-based analysis and bacterial viability stains using confocal microscopy.

The culture results showed that upon exposure to the iodine-based dressings the biofilms were completed eradicated equating to a 6- to 9-Log reduction. In comparison the silver carboxymethylcellulose and methylene blue and gentian violet polyvinyl alcohol foam dressings exhibited signs of bacterial growth post treatment and achieved only a maximum reduction of 3-Log. Furthermore, during microscopy all the samples treated with iodine and silver demonstrated a sharp decrease in the abundance of viable cells whilst the number of non-viable cells dramatically increased.

In contrast, the methylene blue and gentian violet polyvinyl alcohol foam dressing treated biofilms did not exhibit any noticeably change in viability and portrayed similar characteristics to the untreated control micrographs. The viability stains, which differentiate between cell membrane integrity, indicated substantial cell membrane disruption activity by the iodine-based and silver-based dressings. Whilst both silver-based and methylene blue and gentian violet polyvinyl alcohol foam dressings have antibiofilm properties against the strains shown here, the iodine-based dressing demonstrated significantly improved potency.