Characterization of virulence gene expression in different Staphylococcus aureus mastitis isolates

  • Carmen Wolf, Institut für Mikrobiologie, Universität Greifswald, Germany
  • Ines Burghardt, Institut für Mikrobiologie, Universität Greifswald, Germany
  • Christof von Eiff, Institut für Medizinische Mikrobiologie, Universitätsklinikum Münster, Germany
  • Silva Holtfreter, Institut für Immunologie und Transfusionsmedizin, Universität Greifswald, Germany
  • Barbara Bröker, Institut für Immunologie und Transfusionsmedizin, Universität Greifswald, Germany
  • Wolfram Petzl, Klinik für Wiederkäuer mit Ambulanz und Bestandsbetreuung der LMU München, Oberschleißheim, Germany
  • Michael Hecker, Institut für Mikrobiologie, Universität Greifswald, Germany
  • Susanne Engelmann, Institut für Mikrobiologie, Universität Greifswald, Germany

    • Mastitis is the inflammation of the mammary gland and can occur in all mammals. In breastfeeding women as well as in lactating farm animals it is a serious and unpleasant disease. Particularly in dairy cattle, mastitis causes enormous costs to the dairy industry.
    Staphylococcus aureus is one of the most prevalent pathogens causing subclinical mastitis and is well-known for its diversity in the equipment with virulence factors which are supposed to account for the pathogenesis. Extracellular as well as surface associated proteins represent a pool of virulence factors. Thus, the comprehensive analysis of these proteins in different S. aureus isolates may reveal whether there are virulence factors that might be specific for mastitis isolates. Moreover, proteins involved in the particular interaction of S. aureus with the respective host (human or cattle) are of great interest.
    In this study 23 S. aureus mastitis isolates of either bovine (16 isolates) or human (7 isolates) origin were analyzed. We performed genetic and epidemiological studies by using the well established Multi-Locus-Sequence-Typing (MLST) technique as well as Multiplex PCR for determining the agr type and the presence of some virulence genes (e.g. superantigens, eta, etd).
    For the investigation of virulence gene expression in different mastitis isolates, the 2D-PAGE has proved to be a successful tool. The comparison of the extracellular protein patterns resulted in a high heterogeneity between human and bovine strains as well as within strains from the same origin. Altogether 9 extracellular proteins were found in at least 80% of the bovine isolates e.g. autolysin (Atl), alpha-hemolysin precursor (Hla), aureolysin (Aur), SspA and SspB. 17 extracellular proteins could be detected in less than 20% of the bovine isolates, including Leukotoxin E subunit (LukE), three staphylococcal enterotoxins (SEC2, SEC-bov and SEL) and the toxic shock syndrome toxin TSST-1. To ascertain the activity of superantigens, we investigated the influence of supernatants containing extracellular virulence factors/superantigens on the proliferation of (human and bovine) T-cells. For the majority of the isolates we found a correlation between the presence of genes encoding superantigens and the proliferation of T-cells.