Staphylococcus pseudintermedius expresses surface proteins that closely resemble those from Staphylococcus aureus

Staphylococcus pseudintermedius is a commensal of dogs that is implicated in the pathogenesis of canine pyoderma. This study aimed to determine if S. pseudintermedius expresses surface proteins resembling those from Staphylococcus aureus and to characterise them. S. pseudintermedius strain 326 was shown to adhere strongly to purified fibrinogen, fibronectin and cytokeratin 10. It adhered to the α-chain of fibrinogen which, along with binding to cytokeratin 10, is the hallmark of clumping factor B of S. aureus, a surface protein that is in part responsible for colonisation of the human nares. Ligand-affinity blotting with cell-wall extracts demonstrated that S. pseudintermedius 326 expressed a cell-wall anchored fibronectin binding protein which recognised the N-terminal 29 kDa fragment. The ability to bind fibronectin is an important attribute of pathogenic S. aureus and is associated with the ability of S. aureus to colonise skin of human atopic dermatitis patients. S. pseudintermedius genomic DNA was probed with labelled DNA amplified from the serine-aspartate repeat encoding region of clfA of S. aureus. This probe hybridised to a single SpeI fragment of S. pseudintermedius DNA. In the cell-wall extract of S. pseudintermedius 326, a 180 kDa protein was discovered which bound to fibrinogen by ligand-affinity blotting and reacted in a Western blot with antibodies raised against the serine-aspartate repeat region of ClfA and the B-repeats of SdrD of S. aureus. It is proposed that this is an Sdr protein with B-repeats that has an A domain that binds to fibrinogen. Whether it is the same protein that binds cytokeratin 10 is not clear.