Yet more information from our colleagues Johani et al down under support the contention that it’s not what you put on a wound that heals it, but what you take off. Mature biofilms seem to scoff at antimicrobial cleansers.
Summary of key findings
We systematically tested the performance of topical antimicrobial solutions using short exposure times for in vitro and ex vivo models and an in vivo human trial. Our results suggest that the performance of these solutions is poor when challenged against mature biofilms using short exposure times that mimic real clinical use (i.e. 15 min application). Clinicians using topical antimicrobials to cleanse chronic wounds as a single therapy under the assumption of removing biofilm may therefore experience poor clinical outcomes. Clinicians should consider multifaceted strategies that include sharp debridement as the gold standard.
Test the performance of topical antimicrobial wound solutions against microbial biofilms using in vitro, ex vivo and in vivo model systems at clinically relevant exposure times.
Topical antimicrobial wound solutions were tested under three different conditions: (in vitro) 4% w/v Melaleuca oil, polyhexamethylene biguanide, chlorhexidine, povidone iodine and hypochlorous acid were tested at short duration exposure times for 15 min against 3 day mature biofilms of Staphylococcus aureus and Pseudomonas aeruginosa; (ex vivo) hypochlorous acid was tested in a porcine skin explant model with 12 cycles of 10 min exposure, over 24 h, against 3 day mature P. aeruginosa biofilms; and (in vivo) 4% w/v Melaleuca oil was applied for 15 min exposure, daily, for 7 days, in 10 patients with chronic non-healing diabetic foot ulcers complicated by biofilm.
In vitro assessment demonstrated variable efficacy in reducing biofilms ranging from 0.5 log10 reductions to full eradication. Repeated instillation of hypochlorous acid in a porcine model achieved <1 log10 reduction (0.77 log10, P = 0.1). Application of 4% w/v Melaleuca oil in vivo resulted in no change to the total microbial load of diabetic foot ulcers complicated by biofilm (median log10 microbial load pre-treatment = 4.9 log10 versus 4.8 log10, P = 0.43).
Short durations of exposure to topical antimicrobial wound solutions commonly utilized by clinicians are ineffective against microbial biofilms, particularly when used in vivo. Wound solutions should not be used as a sole therapy and clinicians should consider multifaceted strategies that include sharp debridement as the gold standard.