title: Vancomycin-intermediate Staphylococcus aureus isolates are attenuated for virulence when compared with susceptible progenitors.
abstract: OBJECTIVE
  Vancomycin-intermediate Staphylococcus aureus (VISA) is associated with genetic changes that may also impact upon pathogenicity. In the current study, we compared the virulence of clinical VISA strains with their isogenic vancomycin-susceptible progenitors (VSSA).
  
  
  METHODS
  Production of the critical virulence protein, α toxin, was assessed using Western blot analysis and was correlated to agr activity using a bioluminescent agr-reporter. Cytotoxicity and intracellular persistence were compared ex vivo for VSSA and VISA within non-professional phagocytes (NPP). Virulence and host immune responses were further explored in vivo using a murine model of bacteraemia.
  
  
  RESULTS
  VISA isolates produced up to 20-fold less α toxin compared with VSSA, and this was corroborated by either loss of agr activity due to agr mutation, or altered agr activity in the absence of mutation. VISA were less cytotoxic towards NPP and were associated with enhanced intracellular persistence, suggesting that NPP may act as a reservoir for VISA. Infection with VSSA strains produced higher mortality in a murine bacteraemia model (≥90% 7-day mortality) compared with infection with VISA isolates (20% to 50%, p <0.001). Mice infected with VISA produced a dampened immune response (4.6-fold reduction in interleukin-6, p <0.001) and persistent organ bacterial growth was observed for VISA strains out to 7 days.
  
  
  CONCLUSIONS
  These findings highlight the remarkable adaptability of S. aureus, whereby, in addition to having reduced antibiotic susceptibility, VISA alter the expression of pathogenic factors to circumvent the host immune response to favour persistent infection over acute virulence.
authors.affiliation: Infection and Immunity Program, Monash Biomedicine Discovery Institute and Department of Microbiology, Monash University, Australia.
authors.forename: D R
authors.initials: DR
authors.lastname: Cameron
authors.affiliation: Department of Microbiology and Immunology, The University of Melbourne at the Doherty Institute of Infection & Immunity, Australia.
authors.forename: Y-H
authors.initials: YH
authors.lastname: Lin
authors.affiliation: Department of Microbiology, French National Reference Centre for Staphylococci, Hospices Civils de Lyon, International Centre of Infectiology Research, France.
authors.forename: S
authors.initials: S
authors.lastname: Trouillet-Assant
authors.affiliation: Department of Microbiology, French National Reference Centre for Staphylococci, Hospices Civils de Lyon, International Centre of Infectiology Research, France.
authors.forename: V
authors.initials: V
authors.lastname: Tafani
authors.affiliation: Infection and Immunity Program, Monash Biomedicine Discovery Institute and Department of Microbiology, Monash University, Australia.
authors.forename: X
authors.initials: X
authors.lastname: Kostoulias
authors.affiliation: Department of Surgery, The University of Melbourne, Australia.
authors.forename: E
authors.initials: E
authors.lastname: Mouhtouris
authors.affiliation: Department of Medicine, The University of Melbourne, Australia.
authors.forename: N
authors.initials: N
authors.lastname: Skinner
authors.affiliation: Department of Medicine, The University of Melbourne, Australia.
authors.forename: K
authors.initials: K
authors.lastname: Visvanathan
authors.affiliation: Department of Microbiology and Immunology, The University of Melbourne at the Doherty Institute of Infection & Immunity, Australia.
authors.forename: S L
authors.initials: SL
authors.lastname: Baines
authors.affiliation: Department of Microbiology and Immunology, The University of Melbourne at the Doherty Institute of Infection & Immunity, Australia.
authors.forename: B
authors.initials: B
authors.lastname: Howden
authors.affiliation: Department of Microbiology and Immunology, The University of Melbourne at the Doherty Institute of Infection & Immunity, Australia.
authors.forename: I R
authors.initials: IR
authors.lastname: Monk
authors.affiliation: Department of Microbiology, French National Reference Centre for Staphylococci, Hospices Civils de Lyon, International Centre of Infectiology Research, France.
authors.forename: F
authors.initials: F
authors.lastname: Laurent
authors.affiliation: Department of Microbiology and Immunology, The University of Melbourne at the Doherty Institute of Infection & Immunity, Australia.
authors.forename: T P
authors.initials: TP
authors.lastname: Stinear
authors.affiliation: Department of Microbiology and Immunology, The University of Melbourne at the Doherty Institute of Infection & Immunity, Australia; Infectious Diseases and Microbiology Departments, Austin Health, Australia. Electronic address: bhowden@unimelb.edu.au.
authors.forename: B P
authors.initials: BP
authors.lastname: Howden
authors.affiliation: Infection and Immunity Program, Monash Biomedicine Discovery Institute and Department of Microbiology, Monash University, Australia; Department of Infectious Diseases, The Alfred Hospital and Central Clinical School, Monash University, Australia. Electronic address: anton.peleg@monash.edu.
authors.forename: A Y
authors.initials: AY
authors.lastname: Peleg
mesh_terms: D000818:Animals; D016470:Bacteremia / Q000382:microbiology / Q000473:pathology*; D001426:Bacterial Proteins / Q000032:analysis; D001427:Bacterial Toxins / Q000032:analysis; D015153:Blotting, Western; D002460:Cell Line; D002470:Cell Survival; D004195:Disease Models, Animal; D005260:Female; D006460:Hemolysin Proteins / Q000032:analysis; D006801:Humans; D008163:Luminescent Measurements; D008807:Mice, Inbred BALB C; D050296:Microbial Viability; D010586:Phagocytes / Q000276:immunology / Q000382:microbiology; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000472:pathogenicity*; D015534:Trans-Activators / Q000032:analysis; D020713:Vancomycin Resistance; D014774:Virulence
chemical_list: C095698:Agr protein, Staphylococcus aureus; D001426:Bacterial Proteins; D001427:Bacterial Toxins; D006460:Hemolysin Proteins; D015534:Trans-Activators; C021091:staphylococcal alpha-toxin
keywords: Accessory gene regulator; Persistence; Staphylococcus aureus; Vancomycin-intermediate Staphylococcus aureus; Virulence; agr; α toxin