The use of wound dressings as a means to alter the composition of biofilms in a chronic wound model

It is estimated that £5 billion are invested yearly into chronic wound management by the NHS. Whilst the demand for treatment rises every year, it has become harder to treat wounds given the burden of antimicrobial resistance. Chronic wounds can easily become harbouring grounds for polymicrobial biofilms in which species interact in specific ways. This study assessed the interactions between two commonly co-isolated chronic wound pathogens: Pseudomonas aeruginosa (ATCC 9027) and Staphylococcus aureus (EMRSA 15), whose biofilm relation initiates a Gram-negative shift. During this phenomenon, P. aeruginosa takes over the majority of the bacterial community, at the detriment of S. aureus . The Gram-negative shift marks the turning point from an acute to a chronic wound. The pH of a chronic wound is typically alkaline, and it was hypothesised that topical dressings with an acidic pH could disrupt the onset of the Gram negative shift, and therefore chronicity. Six different topical dressings with low pH were used in achronic wound model to assess their ability to reverse or delay the Gram-negative shift. It was found that they did not have an impact on the onset of the Gram-negative shift, despite their low pH values. However, the lower the pH of the dressings, the more frequently small colony variant (SCV) bacteria were observed in the biofilm. SCVs are known for causing persistent or chronic infections. It was therefore concluded that low pH dressings alone may not be favourable for managing chronic wound infection.