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Antimicrobial Agents and Chemotherapy, November 2004, p. 4360-4365, Vol. 48, No. 11
0066-4804/04/$08.00+0     DOI: 10.1128/AAC.48.11.4360-4365.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Usnic Acid, a Natural Antimicrobial Agent Able To Inhibit Bacterial Biofilm Formation on Polymer Surfaces

I. Francolini,^1,2 P. Norris,¹ A. Piozzi,² G. Donelli,³ and P. Stoodley^1,4*

Center for Biofilm Engineering, Montana State University—Bozeman, Bozeman, Montana,¹ Department of Chemistry, University of Rome "La Sapienza,",² Department of Technologies and Health, Istituto Superiore di Sanità, Rome, Italy,³ Center for Genomic Sciences, Allegheny-Singer Research Institute, Pittsburgh, Pennsylvania⁴

Received 9 February 2004/ Accepted 11 July 2004

In modern medicine, artificial devices are used for repair or replacement of damaged parts of the body, delivery of drugs, and monitoring the status of critically ill patients. However, artificial surfaces are often susceptible to colonization by bacteria and fungi. Once microorganisms have adhered to the surface, they can form biofilms, resulting in highly resistant local or systemic infections. At this time, the evidence suggests that (+)-usnic acid, a secondary lichen metabolite, possesses antimicrobial activity against a number of planktonic gram-positive bacteria, including Staphylococcus aureus, Enterococcus faecalis, and Enterococcus faecium. Since lichens are surface-attached communities that produce antibiotics, including usnic acid, to protect themselves from colonization by other bacteria, we hypothesized that the mode of action of usnic acid may be utilized in the control of medical biofilms. We loaded (+)-usnic acid into modified polyurethane and quantitatively assessed the capacity of (+)-usnic acid to control biofilm formation by either S. aureus or Pseudomonas aeruginosa under laminar flow conditions by using image analysis. (+)-Usnic acid-loaded polymers did not inhibit the initial attachment of S. aureus cells, but killing the attached cells resulted in the inhibition of biofilm. Interestingly, although P. aeruginosa biofilms did form on the surface of (+)-usnic acid-loaded polymer, the morphology of the biofilm was altered, possibly indicating that (+)-usnic acid interfered with signaling pathways.

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* Corresponding author. Mailing address: Center for Genomic Sciences, Allegheny-Singer Research Institute, 320 East North Ave., Pittsburgh, PA 15212-4772. Phone: (412) 359-6876. Fax: (412) 359-6995. E-mail: pstoodle{at}wpahs.org.

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Antimicrobial Agents and Chemotherapy, November 2004, p. 4360-4365, Vol. 48, No. 11
0066-4804/04/$08.00+0     DOI: 10.1128/AAC.48.11.4360-4365.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

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