N-acetyl-cysteine Disassembles Bacterial Biofilm And Causes Cell Death Leading To Disappearance Of The Biofilm And Improved Wound Healing
Xin C. Li, Amanda Tedesco, Jane H. Kim, Manuela Martins-Green.
University of California Riverside, Riverside, CA, USA.
Chronic ulcers have become a major challenge to healthcare systems worldwide. The presence of biofilm significantly prevents healing of chronic wounds, suggesting the need to prevent biofilm development or, if present, dismantling the biofilm without adversely affecting the host cells. Despite the availability of various treatments for chronic wound biofilm from antibiotics, to antiseptics, to chlorine and oxygen reactive species, none of them are effective in dismantling biofilm and simultaneously killing the bacteria. We have previously shown that N-acetyl-cysteine (NAC) significantly improves the healing of biofilm-containing chronic wounds in a diabetic mouse model. NAC dismantles the extracellular polymeric substance (EPS) of the biofilm and leads to disappearance of the bacteria from the wounds resulting in healing. We hypothesize that NAC creates an environment that disrupts phenazine binding to eDNA and/or proteins leading to dismantling of the biofilm and that it lowers the pH causing death of the bacteria embedded in the EPS. To test this hypothesis, we performed studies in vitro using biofilm from the chronic wounds of our mouse model containing primarily Pseudomonas aeruginosa. When NAC was added to developed biofilm, we found that the biofilm dismantled and the bacteria in it did not grow in rich media. This effect was dose dependent, with the most effective doses of NAC being the ones that create a pH close to or below the NAC pKa. A similar effect was seen when NAC was added before biofilm formation. Staining with pHrodo Red AM intracellular pH indicator showed that the bacteria cytosol stained intensely suggesting that the pH is low and may indicate bacterial cell death. These results suggest that NAC disrupts biofilm structure and bacterial survival by unbalancing the biofilm oxidative state. These findings may provide guidance to develop new antimicrobials and effective treatments of diabetic chronic wounds.
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