We provide new monoclonal antibody inhibitors of coagulases for treatment of S. aureus. The monoclonal antibodies are useful in targeting the SC N-terminus and inhibiting prothrombin activation. The monoclonal antibodies are able to bind to and interfere with, modulate, and/or inhibit the binding interactions between the staphylocoagulase protein and its ligand protein prothrombin in blood and tissues. The antibodies are effective in inhibiting the activation of prothrombin.