Staphylococcus aureus stimulates urokinase-type plasminogen activator expression by bovine mammary cells

Staphylococcus aureus commonly causes bovine mastitis, but bovine strains, unlike human isolates of S. aureus, do not produce the bacterial plasminogen activator, staphylokinase. By use of bovine mammary epithelial and myoepithelial cell lines, it was found that bovine S. aureus M60 and its culture filtrates induce a 3- to 10-fold increase in urokinase-type plasminogen activator activity in mammary cell-conditioned media and cellular lysates. Furthermore, transcytosis of S. aureus M60 across a mammary epithelial cell monolayer was significantly enhanced by the addition of bovine plasminogen and inhibited by aprotinin. These findings provide evidence that S. aureus M60 can trigger superactivation of host plasminogen activator production and may then utilize the plasminogen activator-plasmin(ogen) system to facilitate tissue invasion without producing staphylokinase.