Successful effectiveness of a thermo-reversible hydrogel against biofilms with differing dressings

Introduction: Biofilms are a common problem in chronic wounds. A thermo-reversible antimicrobial hydrogel (TRH) containing polyhexanide (PHMB) has previously been shown to be effective against of biofilms when tested using in vitro models. PHMB, a positively charged polymer can strongly interact with negatively charged bacterial membrane components leading to increased permeability and loss of integrity. Upon entry into cytoplasm, it can disrupt metabolism and bind to DNA. Use of a negatively charged dressing like alginate can potentially interfere with activity of PHMB. The objective of this study was to evaluate the effectiveness of a TRH with PHMB against wound related organisms using ex vivo porcine skin explant model and differing dressings.Methods:Mature biofilms of Escherichia coli and Staphylococcus epidermidis were developed on porcine skin explant and treated with TRH for up to 7 days and viable numbers were determined at day 1, 3 and 7 to mimic potential dressing change intervals. Mature biofilms of S. aureus, E. coli and S. epidermidis were developed using colony biofilm model treated with TRH and alginate or TRH and cotton dressing for up to 7 days at 37°C. Alginate or cotton dressing treatments without TRH and untreated control were also maintained. Viable numbers were determined at day 1, 3 and 7.Results:TRH reduced viable numbers of E. coli and S. epidermidis ≥6 log CFU by day 7 when tested using porcine skin explant model.  TRH and cotton dressings caused ≥5 log CFU reduction while treatment with TRH and alginate dressing caused ≥4 log CFU reduction of test organisms. These reductions were significantly lower than TRH treatment alone.  Discussion: Since porcine skin explants are structurally similar to human skin, biofilms of E. coli and S. epidermidis were successfully developed using this model. TRH was effective at reducing bioburden of E. coli and S. epidermidis biofilm, suggesting it may potentially be useful tool for combating biofilms in chronic wounds. Although alginate dressing reduced effectiveness of TRH against biofilm, successful bioburden reduction was still observed.References:Malone, M., Bjarnsholt, T., McBain, A.J, James GA, Stoodley P, Leaper D, Tachi M, Schultz G, Swanson T, Wolcott RD. The prevalence of biofilms in chronic wounds: a systematic review and meta-analysis of published data. J Wound Care. 2017 Jan 2;26(1):20-25. doi: 10.12968/jowc.2017.26.1.20. PMID: 28103163. Hübner NO, Kramer A. Review on the efficacy, safety and clinical applications of polihexanide, a modern wound antiseptic. Skin Pharmacol Physiol. 2010;23 Suppl:17-27. doi: 10.1159/000318264. Epub 2010 Sep 8. PMID: 20829658.