B-242. A Novel Staphylococcus aureus Biofilm Phenotype Mediated by the Fibronectin Binding proteins, FnBPA and FnBPB

C. Pozzi1, E. O' Neill1, P. J. Houston1, H. Humphreys2, A. Loughman3, A. D. Robinson4, T. J. Foster3, J. P. O'Gara1;
1Univ. Coll., Dublin, IRELAND, 2Royal Coll. of Surgeons in Ireland, Dublin, IRELAND, 3Moyne Inst. of Preventive Med., Trinity Coll., Dublin, IRELAND, 4New York Med. Coll., Valhalla, NY.

Device-associated infections involving biofilm remain a persistent clinical problem. We recently reported that methicillin-resistant Staphylococcus aureus (MRSA) strains can form biofilm independent of the icaADBC-encoded exopolysaccharide. Here we report that mutation of sortase, which anchors LPXTG-containing proteins to peptidoglycan, impaired MRSA biofilm development. Furthermore deletion of fnbA and fnbB, which encode the LPXTG-anchored multifunctional fibrinogen and fibronectin-binding proteins, FnBPA and FnBPB impaired MRSA but not methicillin-sensitive S. aureus (MSSA) biofilm development, apparently at the level of intercellular accumulation and not primary attachment. The MRSA fnbAB biofilm defect was complemented by fnbA or fnbB alone. Correspondingly, mutation of fnbA or fnbB alone did not substantially affect biofilm and overexpression of either gene alone in MRSA and MSSA activated biofilm. Interestingly FnBP-promoted biofilm was dependent on SarA, but not at the level of fnbA or fnbB transcription. Using plasmid constructs lacking regions of FnBPA to complement an fnbAB mutant revealed that the A domain alone and not the BCD domain required for fibronectin binding could promote biofilm. Additionally, an A domain N304A substitution which abolished fibrinogen binding did not affect biofilm. These data identify a novel S. aureus biofilm phenotype promoted by FnBPA and FnBPB, which is apparently independent of the known ligand-binding activities of these multifunctional surface proteins.