S. MANCINI¹, F. OECHSLIN¹, C. MENZI¹, Y.A. QUE¹, T.R. VELOSO², P. MOREILLON¹, J.M. ENTENZA<sup>1

1</sup>Department of Fundamental Microbiology, UNIL, Lausanne, Switzerland, ²Department of Cardiovascular Sciences, KU Leuven, Leuven, Belgium

Staphylococcus aureus is the most frequent causative agent of infective endocarditis (IE). S. aureus possesses several cell-wall associated proteins, such as the fibrinogen-binding protein ClfA, and secreted plasma-clotting factors such as staphylocoagulase (Coa) and von Willebrand factor binding protein (vWbp). The critical role of ClfA in promoting IE has been already demonstrated (1). The function of Coa and vWbp in IE pathogenesis, however, has not yet been elucidated. Here we used recombinant Lactococcus lactis expressing S. aureus CoA and vWbp, individually (L. lactis Coa and L. lactis vWbp) or together (L. lactis Coa/vWbp), and a rat model of IE, to investigate the role of Coa and vWbp in the initiation of IE. L. lactis pIL253 (parent) was used as control. Rats with catheter-induced aortic vegetations were inoculated with 106 CFU of each L. lactis. Vegetation infection was assessed 24h later. Like the parent L. lactis pIL253 (0% infected vegetations), L. lactis Coa was unable to promote IE (13% infected vegetations). By contrast, L. lactis vWbp increased the incidence of IE (67% infected vegetations; P= 0.007 vs L. lactis Coa). The association of both Coa and vWbp did not further enhanced valve infection (62%). To further investigate the role of vWbp in IE in its natural context, i.e., in S. aureus possessing ClfA, animals were inoculated with 104 CFU of S. aureus Newman harboring both ClfA and vWbp (ClfA+/vWbp+) or isogenic mutants lacking either ClfA (ClfA-/vWbp+) or vWbp (ClfA+/ vWb‒). While no significant reduction in IE incidence was observed with S. aureus lacking vWbp (64% infected vegetations) as compared with the ClfA+/vWbp+ strain (82% infected vegetations), the absence of ClfA led to a significant decrease in S. aureus infectivity (42% infected vegetations; P= 0.02 vs ClfA+/vWbp+). Taken together these results suggest that: (i) vWbp but not Coa supports S. aureus IE development; (ii) ClfA but not vWBP is essential to initiate this infection; (iii) vWbp in association with ClfA may further promote the emergence of IE.

(1) Moreillon P, Entenza JM, Francioli P, Mc Devitt D, Foster TJ, François P, Vaudaux P. Infect. Immun. 1995;63:4738-4743.