摘要The occurrence of infections and mortality in critically ill patients in Intensive Care Units (ICUs) are as high as 53.9％ and 30.0％,respectively.[1] In the United States,the number of patients who died from hospital-acquired infections exceeds 100,000 and the single-item cost is as high as 25 billion USD[2] per year.A study has demonstrated that colonization of conditional exogenous pathogens within the gut is an important pathologic basis of hospital-acquired infections in critically ill ICU patients.[3] The gut is inhabited by the largest variety of bacteria.On one hand,commensal bacteria can inhibit intestinal colonization of conditional exogenous pathogens,and on the other hand,intestinal bacterial flora plays important roles in immunity,metabolism and nourishment.Here,we address the composition of intestinal bacteria,the mechanism underlying decolonization of pathogens in the gut,change in the intestinal micro-ecological environment under pathologic conditions,and maintenance of the ability of the gut in decolonizing pathogenic microbiota.