[Source: Antimicrobial Agents and Chemotherapy, full text: (LINK). Abstract, edited.]
Extracellular DNA shields against aminoglycosides in Pseudomonas aeruginosa biofilms.

Wen-Chi Chiang 1, Martin Nilsson 1, Peter ?strup Jensen 2, Niels H?iby 1,2, Thomas E. Nielsen 3,4, Michael Givskov 1,4 and Tim Tolker-Nielsen 1,*

Author Affiliations: <SUP>1</SUP>Department of International Health, Immunology and Microbiology. Faculty of Health and Medical Sciences. University of Copenhagen. Copenhagen, Denmark <SUP>2</SUP>Department of Clinical Microbiology, University Hospital, Rigshospitalet, Copenhagen, Denmark <SUP>3</SUP>Department of Chemistry, Technical University of Denmark, Kgs. Lyngby, Denmark <SUP>4</SUP>Singapore Centre on Environmental Life Sciences Engineering, Nanyang Technological University, Singapore


Within recent years it has been established that extracellular DNA is a key constituent of the matrix of microbial biofilms. In addition, it has recently been demonstrated that DNA binds positively charged antimicrobials such as aminoglycosides and antimicrobial peptides. In the present study we provide evidence that extracellular DNA shields against aminoglycosides in Pseudomonas aeruginosa biofilms. We show that exogenously supplemented DNA integrates into P. aeruginosa biofilms and increases their tolerance towards aminoglycosides. We provide evidence that biofilms formed by a DNA-release deficient P. aeruginosa quorum-sensing mutant are more susceptible to aminoglycoside treatment than wild type biofilms, but become rescued from the detrimental action of aminoglycosides upon supplementation with exogenous DNA. Furthermore, we demonstrate that exposure to lysed polymorphonuclear leukocytes, which are thought to be a source of extracellular DNA at sites of infections, increases the tolerance of P. aeruginosa biofilms towards aminoglycosides. Although biofilm-associated aminoglycoside tolerance recently has been linked to extracellular DNA-mediated activation of the pmr genes, we demonstrate that the aminoglycoside tolerance mediated by the presence of extracellular DNA is not caused by activation of the pmr genes in our P. aeruginosa biofilms, but rather by a protective shield effect of the extracellular DNA.


*Corresponding author: Tim Tolker-Nielsen., Mailing address: Department of International Health, Immunology and Microbiology., Faculty of Health Sciences, University of Copenhagen., Blegdamsvej 3B, DK-2200 Copenhagen N, Denmark, Phone: +45 353 26656., E-mail: ttn@sund.ku.dk.

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