The same problem occurs in Respiratory Care Centers (RCCs) which are designed to care the patients with prolonged mechanical ventilation (PMV), MV for more than 21 days, in Taiwan. One report from Taiwan showed that nosocomial infection rate in RCC is about 40% and the patients develop nosocomial infection have lower weaning rate and higher mortality compared with the patients without infection [2]. It has been estimated that 50% to 60% the nosocomial infection occurring each year in the United Sates are caused by antibiotic-resistant bacterial strains [3]. This high rate of resistant strains increases the morbidity, mortality and medical costs of infection. Preventing infection and limiting the emergence of antibiotic-resistant strains are two important issues in critical care medicine.