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Anti-infectives used to treat chronic exuding wounds are diluted by wound exudates, absorbed into dressings, metabolised by proteases and destroyed by pH. In order to mimic such effects of exudates, the efficacy of six topical wound agents was assessed undiluted and at 10% concentrations, including povidone-iodine ointment and a silver-impregnated wound dressing, to remove biofilms of Pseudomonas aeruginosa, multi-species biofilms of Candida albicans and methicillin-resistant Staphylococcus aureus (MRSA) in vitro in a Centers for Disease Control and Prevention (CDC) reactor. Povidone-iodine was also diluted to 3⋅3% and 33⋅3% of the commercial concentrations. Viable microorganisms in each preparation were quantified by colony count. No viable P. aeruginosa biofilm material was recovered after 4 and 24 hours of treatment with povidone-iodine ointment at the 100% and 10% concentrations. No C. albicans/MRSA biofilm material was recovered after 4 and 24 hours of treatment with povidone-iodine ointment at the 100% concentration. In general, following dilution, povidone-iodine ointment appeared to exhibit greater biofilm removal than the other agents tested. Further research involving different microorganisms in vitro and in vivo over a longer period of time will help elucidate the full potential of povidone-iodine ointment and liposomal hydrogel.

Bacterial toxins are thought to play a role in delayed wound healing in critically colonised and infected wounds. Endotoxins are released from Gram-negative bacteria when they are lysed by host phagocytic cells during an immune response, or by antimicrobial agents, potentially leading to a detrimental effect on the host tissues. Endotoxins can affect all aspects of the wound healing process, leading to delayed healing and contributing to wound chronicity. Release of endotoxins by bacteria can also have serious systemic effects (for example, septic shock) that can lead to high levels of patient mortality. This review summarises the role and implications on wound healing of bacterial endotoxins, describing the impact of endotoxins on the various phases of the wound healing response. There is a paucity of in vivo/clinical evidence linking endotoxins attributed to a wound (via antibiotic treatment) or their release from infecting bacteria with parameters of delayed wound healing. Future work should investigate if this link is apparent and determine the mechanism(s) by which such detrimental effects occur, offering an opportunity to identify possible treatment pathways. This paper describes the phenomenon of antimicrobial-induced endotoxin release and summarises the use of wound dressings to reduce wound bioburden without inducing microbial death and subsequent release of endotoxins, thus limiting their detrimental effects.

Objective: To assess the in vitro antimicrobial performance of a non-medicated hydro-responsive wound dressing (HRWD) on the sequestration and killing of wound relevant microorganisms found on the World Health Organization (WHO) priority pathogens list. Methods: Suspensions of Pseudomonas aeruginosa, Acinetobacter baumannii and methicillin-resistant Staphylococcus aureus (MRSA) were placed on petri dishes. Dressings were each placed on top, incubated for 30 minutes and then removed from the inoculated petri dish. The surface of the dressings previously in contact with the bacterial suspensions were placed directly onto a tryptone soy agar (TSA) plate and incubated for 24 hours. Dressings were then removed from the TSA plate and the level of bacterial growth on the plates was assessed. Sequestered microorganism viability was assessed using LIVE/DEAD viability kits and visualisation by epifluorescence. Results: Our results indicated that HRWDs sequester and retain Pseudomonas aeruginosa, Acinetobacter baumannii and MRSA within the dressing. Non-medicated HRWDs containing bound PHMB (polyhexamethylene biguanide, HRWD+PHMB) killed the microorganisms sequestered within the dressing matrix. Conclusion: These data suggest that non-medicated HRWD+PHMB is an effective against WHO priority pathogens and promoting goal of antimicrobial stewardship in wound care.

Objective: To assess the efficacy of five silver-containing gelling fibre wound dressings against single-species and multispecies biofilms using internally validated, UKAS-accredited in vitro test models. Method: Staphylococcus aureus, Pseudomonas aeruginosa and Candida albicans single- and multispecies biofilms were cultured using Centres for Disease Control (CDC) biofilm reactors and colony drip flow reactors (CDFR). Following a 72 hour incubation period, the substrates on which biofilms were grown were rinsed to remove planktonic microorganisms and then challenged with fully hydrated silver-containing gelling fibre wound dressings. Following dressing application for 24 or 72 hours, remaining viable organisms from the treated biofilms were quantified. Results: In single-species in vitro models, all five antimicrobial dressings were effective in eradicating Staphylococcus aureus and Pseudomonas aeruginosa biofilm bacteria. However, only one of the five dressings (Hydrofiber technology with combination antibiofilm/antimicrobial technology) was able to eradicate the more tolerant single-species Candida albicans biofilm. In a more complex and stringent CDFR biofilm model, the hydrofiber dressing with combined antibiofilm/antimicrobial technology was the only dressing that was able to eradicate multispecies biofilms such that no viable organisms were recovered. Conclusion: Given the detrimental effects of biofilm on wound healing, stringent in vitro biofilm models are increasingly required to investigate the efficacy of antimicrobial dressings. Using accredited in vitro biofilm models of increasing complexity, differentiation in the performance of dressings with combined antibiofilm/antimicrobial technology against those with antimicrobial properties alone, was demonstrated.