Nowadays, the programs of infection control can address only one third of nosocomial infections. Therefore, two thirds of these infections are still not controlled, and their cause remain unknown. Hospital or nosocomial infections are defined as a type of infection that occurs within 48 hours of hospital admission, after 3 days of discharge from the hospital or 30 days after an operation. Infections manifested during one year after prosthesis-placement surgery are also considered nosocomial infections. Studies point out that 1 in each 10 patients will acquire a nosocomial infection, which can result in 5.000 deaths in the United States per year. The Center of Disease and Control released a study entitled The Direct medical costs of healthcare-associated infections in U.S. hospitals and the benefits of prevention, in which it is stated that nosocomial Infections costed yearly 28.45 billions of dollars per year.