Silver-zinc EDTA complexes demonstrated significant antibiofilm activity in a complex wound environment with in an in vitro model

Abstract: Aim: Slough, which covers the wound bed, harbors microorganisms and biofilms, prevents the formation of new healthy tissue, and delays wound healing, is hallmark feature of chronic wounds. The aim of this study is to understand the effects of chronic wound environment on the activities of silver-containing complexes (Ag-Zn MMC) in an in vitro slough model. Method: An in vitro artificial wound slough (AWS) -biofilm model which involved a pre-formed Pseudomonas aeruginosa biofilm under a layer of AWS was applied to evaluate the antibacterial/antibiofilm efficacy of Ag-Zn MMC and AgNO3 solutions. The test samples were added directly onto the AWE-biofilm substrate with different thicknesses. The bacterial cell density in the medium was determined by taking a sample and serial diluting in PBS, before plating each dilution onto Tryptone Soya Agar in duplicate after 0, 2.5, 6 and 24 hours. The penetration of the antimicrobial composition (e.g. silver ions) through the AWE membrane was monitored electrochemically using a printed carbon sensor. The disruption of P. aeruginosa biofilm by the treatments was imaged by LSM 780 Zeiss confocal microscope. Results / Discussion: The results showed that silver ions penetrated through the AWS membrane aided by EDTA (chelating agent) to reach the biofilm underneath. The penetration rate of silver ion was inversely proportional to the AWE thickness. The antibiofilm test results indicated that the Ag-Zn MMC had higher antibiofilm efficacy and penetration rates than the AgNO3 solution with same silver concentration. Conclusion: The results demonstrated the potential for the EDTA metal complexes, such as Ag-Zn MMC to be used for treatment and disruption of biofilms, such as those that covered by the slough of chronic wounds.

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