Electroceutical treatment of Pseudomonas aeruginosa biofilms

Abstract

Electroceutical wound dressings, especially those involving current flow with silver based electrodes, show promise for treating biofilm infections. However, their mechanism of action is poorly understood. We have developed an in vitro agar based model using a bioluminescent strain of Pseudomonas aeruginosa to measure loss of activity and killing when direct current was applied. Silver electrodes were overlaid with agar and lawn biofilms grown for 24h. A 6V battery with 1kΩ ballast resistor was used to treat the biofilms for 1h or 24h. Loss of bioluminescence and a 4-log reduction in viable cells was achieved over the anode. Scanning electron microscopy showed damaged cells and disrupted biofilm architecture. The antimicrobial activity continued to spread from the anode for at least 2 days, even after turning off the current. Elemental analysis using Energy Dispersive X-ray Spectroscopic (EDS) analysis through the agar suggests that silver was not responsible for the observed killing. Electrochemistry of silver electrodes in aqueous solutions containing chlorine, pH measurements, the time delay between when the cidal agent is produced and when adverse impact on the biofilm is observed, and chlorotyrosine in the lysates, all suggest that hypochlorous acid was a likely agent in the destruction of these biofilm forming bacteria. Similar killing was obtained with gels containing only bovine synovial fluid or human serum. These results suggest that our in vitro model could serve as a platform for fundamental studies to explore the effects of electrochemical treatment on biofilms, complementing clinical studies with electroceutical dressings.

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ORCID for Paul Stoodley: orcid.org/0000-0001-6069-273X

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