title: Extracellular DNA Acidifies Biofilms and Induces Aminoglycoside Resistance in Pseudomonas aeruginosa.
abstract: Biofilms consist of surface-adhered bacterial communities encased in an extracellular matrix composed of DNA, exopolysaccharides, and proteins. Extracellular DNA (eDNA) has a structural role in the formation of biofilms, can bind and shield biofilms from aminoglycosides, and induces antimicrobial peptide resistance mechanisms. Here, we provide evidence that eDNA is responsible for the acidification of Pseudomonas aeruginosa planktonic cultures and biofilms. Further, we show that acidic pH and acidification via eDNA constitute a signal that is perceived by P. aeruginosa to induce the expression of genes regulated by the PhoPQ and PmrAB two-component regulatory systems. Planktonic P. aeruginosa cultured in exogenous 0.2% DNA or under acidic conditions demonstrates a 2- to 8-fold increase in aminoglycoside resistance. This resistance phenotype requires the aminoarabinose modification of lipid A and the production of spermidine on the bacterial outer membrane, which likely reduce the entry of aminoglycosides. Interestingly, the additions of the basic amino acid L-arginine and sodium bicarbonate neutralize the pH and restore P. aeruginosa susceptibility to aminoglycosides, even in the presence of eDNA. These data illustrate that the accumulation of eDNA in biofilms and infection sites can acidify the local environment and that acidic pH promotes the P. aeruginosa antibiotic resistance phenotype.
authors.affiliation: Department of Microbiology, Immunology and Infectious Diseases, Snyder Institute of Chronic Diseases, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada.
authors.forename: Mike
authors.initials: M
authors.lastname: Wilton
authors.affiliation: Department of Microbiology, Immunology and Infectious Diseases, Snyder Institute of Chronic Diseases, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada.
authors.forename: Laetitia
authors.initials: L
authors.lastname: Charron-Mazenod
authors.affiliation: Department of Microbiology, Immunology and Infectious Diseases, Snyder Institute of Chronic Diseases, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada.
authors.forename: Richard
authors.initials: R
authors.lastname: Moore
authors.affiliation: Department of Microbiology, Immunology and Infectious Diseases, Snyder Institute of Chronic Diseases, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada Faculty of Science and Technology, Athabasca University, Athabasca, Alberta, Canada slewenza@ucalgary.ca.
authors.forename: Shawn
authors.initials: S
authors.lastname: Lewenza
mesh_terms: D000617:Aminoglycosides / Q000494:pharmacology*; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001089:Arabinose / Q000031:analogs & derivatives / Q000378:metabolism; D001120:Arginine / Q000378:metabolism / Q000494:pharmacology; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D018441:Biofilms / Q000187:drug effects* / Q000254:growth & development; D001692:Biological Transport; D004269:DNA, Bacterial / Q000378:metabolism / Q000494:pharmacology*; D024881:Drug Resistance, Bacterial / Q000187:drug effects* / Q000235:genetics; D005110:Extracellular Space / Q000737:chemistry; D015964:Gene Expression Regulation, Bacterial; D006863:Hydrogen-Ion Concentration; D008050:Lipid A / Q000378:metabolism; D008826:Microbial Sensitivity Tests; D010933:Plankton / Q000187:drug effects / Q000254:growth & development; D011550:Pseudomonas aeruginosa / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D017693:Sodium Bicarbonate / Q000378:metabolism / Q000494:pharmacology; D013095:Spermidine / Q000378:metabolism / Q000494:pharmacology; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
chemical_list: D000617:Aminoglycosides; D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D004269:DNA, Bacterial; D008050:Lipid A; C079792:PhoQ protein, Bacteria; C409039:PmrB protein, bacteria; D014157:Transcription Factors; C016982:aminoarabinose; C081902:pmrA protein, Bacteria; C061064:PhoP protein, Bacteria; D017693:Sodium Bicarbonate; D001120:Arginine; D001089:Arabinose; D013095:Spermidine