The purpose of this study is the prevention of Staphylococcus aureus pneumonia in mechanically ventilated subjects heavily colonized with S. aureus. Staphylococcus aureus is a human pathogenic bacterium that causes severe infections, including pneumonia and sepsis. Hospital-acquired bacterial pneumonia (HABP) caused by S. aureus, including ventilator-associated bacterial pneumonia (VABP) in mechanically ventilated subjects, is a significant public health threat despite efforts to optimize antibiotic treatment. ASN100 is an investigational monoclonal antibody product that targets the toxins produced by S. aureus to protect subjects from developing S. aureus pneumonia.