They used it against a bacterium that had learned to protect itself against most of the other drugs thrown at it, a particularly dangerous variety of staph called methicillin-resistant Staphylococcus aureus???MRSA, for short.Staph, the short form of the family name Staphylococcus, is an ancient organism with a vast arsenal of tricks and defenses, some of them newly learned, others as old as man.