title: A Caenorhabditis elegans host model correlates with invasive disease caused by Staphylococcus aureus recovered during an outbreak in neonatal intensive care.
abstract: BACKGROUND
  Caenorhabditis elegans has previously been used as a host model to determine the virulence of clinical methicillin-resistant Staphylococcus aureus isolates. In the present study, methicillin-susceptible S aureus (MSSA) strains associated with an outbreak in a neonatal intensive care unit (NICU) were investigated using the C elegans model.
  
  
  METHODS
  Two distinct outbreak clones, MSSA type-C and MSSA type-G, were identified by pulsed-field gel electrophoresis in a MSSA outbreak during a seven-month period in the NICU of the Sunnybrook Health Sciences Centre (Toronto, Ontario). MSSA type-C was associated with severe infection, while type-G was associated with less invasive disease. Four representative type-C isolates, three type-G and three infant-colonized isolates unrelated to the outbreak, were sent to Calgary (Alberta), for the double-blinded virulence tests in the C elegans host model and for further molecular characterization.
  
  
  RESULTS
  The invasive outbreak strains (type-C) demonstrated highly nematocidal activity, the noninvasive outbreak strains (type-G) an intermediate virulence, and the outbreak-unrelated colonization isolates demonstrated avirulence or low virulence in the C elegans model, with mean killing rates of 93.0%, 61.0% and 14.4% by day 9, respectively, for these three group strains. Different group MSSA strains had their own unique genetic profiles and virulence gene profiles, but all isolates within the same group (type-C or type-G) shared identical genetic characteristics and virulence gene patterns.
  
  
  CONCLUSIONS
  The present blinded evaluation demonstrated that the nematocidal activities of MSSA strains correlated well with the clinical manifestation in an MSSA outbreak in the NICU, supporting C elegans as a robust host model to study the pathogenesis of S aureus.
authors.affiliation: Department of Pathology and Laboratory Medicine; ; Centre for Antimicrobial Resistance, Alberta Health Services/Calgary Laboratory Services/University of Calgary, Calgary, Alberta;
authors.forename: Kaiyu
authors.initials: K
authors.lastname: Wu
authors.forename: Andrew E
authors.initials: AE
authors.lastname: Simor
authors.forename: Mary
authors.initials: M
authors.lastname: Vearncombe
authors.forename: Jo-Ann
authors.initials: JA
authors.lastname: McClure
authors.forename: Kunyan
authors.initials: K
authors.lastname: Zhang
keywords: Caenorhabditis elegans; Double-blinded test; MSSA; Methicillin-suseptible Staphylococcus aureus outbreak; NICU; Neonatal intensive care unit; Staphylococcus aureus; Virulence host model