title: Norlichexanthone Reduces Virulence Gene Expression and Biofilm Formation in Staphylococcus aureus.
abstract: Staphylococcus aureus is a serious human pathogen and antibiotic resistant, community-associated strains, such as the methicillin resistant S. aureus (MRSA) strain USA300, continue to spread. To avoid resistance, anti-virulence therapy has been proposed where toxicity is targeted rather than viability. Previously we have shown that norlichexanthone, a small non-reduced tricyclic polyketide produced by fungi and lichens, reduces expression of hla encoding α-hemolysin as well as the regulatory RNAIII of the agr quorum sensing system in S. aureus 8325-4. The aim of the present study was to further characterise the mode of action of norlichexanthone and its effect on biofilm formation. We find that norlichexanthone reduces expression of both hla and RNAIII also in strain USA300. Structurally, norlichexanthone resembles ω-hydroxyemodin that recently was shown to bind the agr two component response regulator, AgrA, which controls expression of RNAIII and the phenol soluble modulins responsible for human neutrophil killing. We show that norlichexanthone reduces S. aureus toxicity towards human neutrophils and interferes directly with AgrA binding to its DNA target. In contrast to ω-hydroxyemodin however, norlichexanthone reduces staphylococcal biofilm formation. Transcriptomic analysis revealed that genes regulated by the SaeRS two-component system are repressed by norlichexanthone when compared to untreated cells, an effect that was mitigated in strain Newman carrying a partially constitutive SaeRS system. Our data show that norlichexanthone treatment reduces expression of key virulence factors in CA-MRSA strain USA300 via AgrA binding and represses biofilm formation.
authors.affiliation: Department of Veterinary Disease Biology, Faculty of Health and Medical Sciences, University of Copenhagen, Frederiksberg C, Denmark.
authors.forename: Mara
authors.initials: M
authors.lastname: Baldry
authors.affiliation: Department of Veterinary Disease Biology, Faculty of Health and Medical Sciences, University of Copenhagen, Frederiksberg C, Denmark.
authors.forename: Anita
authors.initials: A
authors.lastname: Nielsen
authors.affiliation: Department of Veterinary Disease Biology, Faculty of Health and Medical Sciences, University of Copenhagen, Frederiksberg C, Denmark.
authors.forename: Martin S
authors.initials: MS
authors.lastname: Bojer
authors.affiliation: Chinese Academy of Sciences Key Laboratory of Pathogenic Microbiology and Immunology, Institute of Microbiology, Beijing, China.
authors.forename: Yu
authors.initials: Y
authors.lastname: Zhao
authors.affiliation: Department of Veterinary Disease Biology, Faculty of Health and Medical Sciences, University of Copenhagen, Frederiksberg C, Denmark.
authors.forename: Cathrine
authors.initials: C
authors.lastname: Friberg
authors.affiliation: Department of Veterinary Disease Biology, Faculty of Health and Medical Sciences, University of Copenhagen, Frederiksberg C, Denmark.
authors.forename: Dan
authors.initials: D
authors.lastname: Ifrah
authors.affiliation: Department of Veterinary Disease Biology, Faculty of Health and Medical Sciences, University of Copenhagen, Frederiksberg C, Denmark.
authors.forename: Nina
authors.initials: N
authors.lastname: Glasser Heede
authors.affiliation: Center for Microbial Biotechnology, Department of Systems Biology, Technical University of Denmark, Kongens Lyngby, Denmark.
authors.forename: Thomas O
authors.initials: TO
authors.lastname: Larsen
authors.affiliation: Department of Veterinary Disease Biology, Faculty of Health and Medical Sciences, University of Copenhagen, Frederiksberg C, Denmark.
authors.forename: Hanne
authors.initials: H
authors.lastname: Frøkiær
authors.affiliation: Department of Veterinary Disease Biology, Faculty of Health and Medical Sciences, University of Copenhagen, Frederiksberg C, Denmark.
authors.forename: Dorte
authors.initials: D
authors.lastname: Frees
authors.affiliation: Chinese Academy of Sciences Key Laboratory of Pathogenic Microbiology and Immunology, Institute of Microbiology, Beijing, China.
authors.forename: Lixin
authors.initials: L
authors.lastname: Zhang
authors.affiliation: Chinese Academy of Sciences Key Laboratory of Pathogenic Microbiology and Immunology, Institute of Microbiology, Beijing, China.
authors.forename: Huanqin
authors.initials: H
authors.lastname: Dai
authors.affiliation: Department of Veterinary Disease Biology, Faculty of Health and Medical Sciences, University of Copenhagen, Frederiksberg C, Denmark.
authors.forename: Hanne
authors.identifier: http://orcid.org/0000-0002-8350-5631
authors.initials: H
authors.lastname: Ingmer
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D018441:Biofilms / Q000187:drug effects*; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects*; D006801:Humans; D013203:Staphylococcal Infections / Q000235:genetics / Q000378:metabolism / Q000382:microbiology; D013211:Staphylococcus aureus / Q000235:genetics* / Q000378:metabolism; D014774:Virulence / Q000187:drug effects / Q000235:genetics*; D037521:Virulence Factors / Q000235:genetics*; D044004:Xanthones / Q000494:pharmacology*
chemical_list: D001426:Bacterial Proteins; D037521:Virulence Factors; D044004:Xanthones; C568539:norlichexanthone