I read recently that bacteria, if present, are found on the surface of meat. As long as the surface of the meat is well cooked, it is fine to eat a steak rare. The problem is when the meat is minced and the bacteria is mixed to the centre of the burger. If the centre is not completely cooked, the bacteria will survive..
But if the chef makes the mince from a cut of steak just before he cooks it will this not be O.K.?