The Antimicrobial Efficacy of an Iodine Based Foam Dressing on MRSA and VRE

The wound healing process involves various complex processes which typically are broken down into: the inflammation phase, whereby the wound attempts to expel foreign microbes and other contaminates; the destructive phase, whereby dead tissue is removed; and the maturation phase, in which the wound becomes closed.

Colonisation of wounds by microorganisms can disrupt these processes and significantly delay the length of time required to heal. To combat this, wound dressings incorporated with antimicrobials must demonstrate efficacy against an array of different microbes, in particular antibiotic-resistant isolates.

In this study, we used a silver-based dressing to compare the efficacious properties of an iodine-based dressing and a methylene blue and gentian violet polyvinyl alcohol foam dressing. A log reduction assay for all wound dressings was undertaken following inoculation with 106 CFU/mL of methicillin-resistance Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus faecalis (VRE) and incubated at 37 °C for up to 24 hours; samples of the dressings were removed at 1, 3, 6 and 24 hour time points to evaluate bacterial growth and thus log reduction achieved.

For comparison, an untreated control dressing was used to indicate the bacterial concentration at each sampling point over the 24-hour period; the results showed the control gradually increased from 105 to 109 CFU/mL due to microbial proliferation. Upon exposure to the antimicrobial dressings, the silver and the iodine-based dressings achieved complete inactivation (~4 Log reduction) within 3 and 6 hours for both MRSA and VRE, respectively; whilst the methylene blue and gentian violet polyvinyl dressing was unable to achieve complete inactivation within the 24 hour experiment (P < 0.0001). Iodine-based dressings are known to support the wound healing processes by helping to reduce microbial bioburden, and with no evidence of bacterial resistance, iodine is an important antimicrobial moving forward in future of wound care.