Antimicrobial Hypochlorous Wound Irrigation Solutions Demonstrate Lower Anti-biofilm Efficacy Against Bacterial Biofilm in a Complex in-vitro Human Plasma Biofilm Model (hpBIOM) Than Common Wound Antimicrobials

Abstract

Biofilms pose a relevant factor for wound healing impairment in chronic wounds. With 78% of all chronic wounds being affected by biofilms, research in this area is of high priority, especially since data for evidence-based selection of appropriate antimicrobials and antiseptics is scarce. Therefore, the objective of this study was to evaluate the anti-biofilm efficacy of commercially available hypochlorous wound irrigation solutions compared to established antimicrobials. Using an innovative complex in-vitro human plasma biofilm model (hpBIOM), quantitative reduction of Pseudomonas aeruginosa , Staphylococcus aureus , and Methicillin-resistant S. aureus (MRSA) biofilms by three hypochlorous irrigation solutions [two <0.08% and one 0.2% sodium hypochlorite (NaClO)] was compared to a 0.04% polyhexanide (PHMB) irrigation solution and 0.1% octenidine-dihydrochloride/phenoxyethanol (OCT/PE). Efficacy was compared to a non-challenged planktonic approach, as well as with increased substance volume over a prolonged exposure (up to 72 h). Qualitative visualization of biofilms was performed by scanning electron microscopy (SEM). Both reference agents (OCT/PE and PHMB) induced significant biofilm reductions within 72 h, whereby high volume OCT/PE even managed complete eradication of P. aeruginosa and MRSA biofilms after 72 h. The tested hypochlorous wound irrigation solutions achieved no relevant penetration and eradication of biofilms despite increased volume and exposure. Only 0.2% NaClO managed a low reduction under prolonged exposure. The results demonstrate that low-dosed hypochlorous wound irrigation solutions are significantly less effective than PHMB-based irrigation solution and OCT/PE, thus unsuitable for biofilm eradication on their own. The used complex hpBIOM thereby mimics the highly challenging clinical wound micro-environment, providing a more profound base for future clinical translation.

In vitro Activity of Antimicrobial Wound Dressings on P. aeruginosa Wound Biofilm

“…Even though several studies addressed this issue, most concluded that further analyses are mandatory to gain evidence-based recommendations for the daily use of antimicrobial dressings (Storm-Versloot et al, 2010;Daeschlein, 2013;Forster and Pagnamenta, 2015;Wu et al, 2015;Norman et al, 2016). Using a complex 3D model designed to mimic the micro-environment of a human wound biofilm (lhBIOM), composed of human material (plasma, platelets and leukocytes), this study aimed to extend the knowledge-base on efficacy profiles of antimicrobial wound dressings in a more transferable, "closer-to-reality" test scenario (Besser et al, 2020;Rembe et al, 2020;Stuermer et al, 2021). In this model, the incorporated bacteria encounter not only a milieu similar to the wound exudate (Loeffler et al, 2013), but also a certain immunological competence represented by leukocytes, so a biofilm matrix has to be produced under the challenge of a donor's immunocompetence (Figure 1).…”

“…Lateral resistance gene transfer between species and sub-species, dorment persister cells in the depth of biofilm and tissue as well as an effective biochemical diffusion barrier for active agents are further aspects contributing to the high resilience of microbial biofilms (Percival et al, 2015;Kirketerp-Møller et al, 2020). Even if an antimicrobial substance is capable of effectively eradicating a bacterial strain in its planctonic state, a deep enough penetration to achieve the same reductive efficacy, cannot be ensured in a complex biofilm scenario (Rembe et al, 2020).…”

“…Thus, it is currently unclear whether the anti-biofilm activity of antimicrobial agents embedded in wound dressings is comparable to its antimicrobial liquid counterpart in the wound microenvironment. The presented work addresses this question in vitro using a modified human plasma-based biofilm model (lhBIOM) developed and described earlier by the authors (Besser et al, 2020;Rembe et al, 2020;Stuermer et al, 2021). The model mimics the condition of a wound biofilm by consisting of a bacteria-incorporating, matured, three-dimensional (3D) gel-like biofilm structure surrounded by bacteria-rich human plasma, which is similar to the composition of wound exudate in terms of protein content, carbohydrates, enzymes and bacterial breakdown products (Demidova-Rice et al, 2012;Stuermer et al, 2021).…”

In Vitro Efficacy of Bacterial Cellulose Dressings Chemisorbed with Antiseptics against Biofilm Formed by Pathogens Isolated from Chronic Wounds

“…These discrepancies can be due to using various methods and different concentrations of NaOCl and HOCl. While the antimicrobial activity of high chlorine concentrations is undisputable, the extrapolation of favorable results to all SOH-containing products (regardless of the chlorine content) seems to be inappropriate [ 27 , 79 , 80 , 81 , 82 , 83 ]. There is a lack of evidence for a prolonged time of action of SOH.…”

Trade-offs between antiseptic cytotoxicity and efficacy in a humanex vivowound contamination model

“…Further, classical in vitro models often expose established microbial biofilms in environmental conditions that are divorced from the host context. For example, host-derived biofilm components such as fibrin and leukocyteassociated proteins can alter biofilm composition and structure (Besser et al, 2020;Kwiecinski et al, 2016;Nett et al, 2015;Rembe et al, 2020), with potential effects on antiseptic susceptibility, virulence and pathogenesis. Our model provides a clinically-relevant environmental context for microbial growth.…”