title: Amphibian antimicrobial peptide fallaxin analogue FL9 affects virulence gene expression and DNA replication in Staphylococcus aureus.
abstract: The rapid rise in antibiotic-resistant pathogens is causing increased health concerns, and consequently there is an urgent need for novel antimicrobial agents. Antimicrobial peptides (AMPs), which have been isolated from a wide range of organisms, represent a very promising class of novel antimicrobials. In the present study, the analogue FL9, based on the amphibian AMP fallaxin, was studied to elucidate its mode of action and antibacterial activity against the human pathogen Staphylococcus aureus. Our data showed that FL9 may have a dual mode of action against S. aureus. At concentrations around the MIC, FL9 bound DNA, inhibited DNA synthesis and induced the SOS DNA damage response, whereas at concentrations above the MIC the interaction between S. aureus and FL9 led to membrane disruption. The antibacterial activity of the peptide was maintained over a wide range of NaCl and MgCl(2) concentrations and at alkaline pH, while it was compromised by acidic pH and exposure to serum. Furthermore, at subinhibitory concentrations of FL9, S. aureus responded by increasing the expression of two major virulence factor genes, namely the regulatory rnaIII and hla, encoding α-haemolysin. In addition, the S. aureus-encoded natural tolerance mechanisms included peptide cleavage and the addition of positive charge to the cell surface, both of which minimized the antimicrobial activity of FL9. Our results add new information about FL9 and its effect on S. aureus, which may aid in the future development of analogues with improved therapeutic potential.
authors.affiliation: Department of Veterinary Disease Biology, Faculty of Health and Medical Sciences, University of Copenhagen, DK-1870 Frederiksberg, Denmark.
authors.forename: Sanne
authors.initials: S
authors.lastname: Gottschalk
authors.affiliation: National Institute of Aquatic Resources, Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark.
authors.forename: Caroline T
authors.initials: CT
authors.lastname: Gottlieb
authors.affiliation: Department of Veterinary Disease Biology, Faculty of Health and Medical Sciences, University of Copenhagen, DK-1870 Frederiksberg, Denmark.
authors.forename: Martin
authors.initials: M
authors.lastname: Vestergaard
authors.affiliation: Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, DK-2100 Copenhagen, Denmark.
authors.forename: Paul R
authors.initials: PR
authors.lastname: Hansen
authors.affiliation: Department of Systems Biology, Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark.
authors.forename: Lone
authors.initials: L
authors.lastname: Gram
authors.affiliation: Department of Veterinary Disease Biology, Faculty of Health and Medical Sciences, University of Copenhagen, DK-1870 Frederiksberg, Denmark.
authors.forename: Hanne
authors.initials: H
authors.lastname: Ingmer
authors.affiliation: Department of Veterinary Disease Biology, Faculty of Health and Medical Sciences, University of Copenhagen, DK-1870 Frederiksberg, Denmark.
authors.forename: Line E
authors.initials: LE
authors.lastname: Thomsen
mesh_terms: D023181:Antimicrobial Cationic Peptides / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D002462:Cell Membrane; D004261:DNA Replication / Q000187:drug effects*; D004269:DNA, Bacterial / Q000378:metabolism*; D024881:Drug Resistance, Bacterial; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects*; D008826:Microbial Sensitivity Tests; D013014:SOS Response, Genetics; D013211:Staphylococcus aureus / Q000187:drug effects*; D037521:Virulence Factors / Q000235:genetics / Q000378:metabolism*
chemical_list: D023181:Antimicrobial Cationic Peptides; D001426:Bacterial Proteins; D004269:DNA, Bacterial; C000606777:FL9 peptide; D037521:Virulence Factors