Topic I: “The intestinal flora” discusses the microbial population of the human digestive tract. This part also provides information concerning the quantitative and qualitative characterization of this ecosystem, the interaction between gut bacteria, intestine and host immunity. In particular, this topic explain the important role that the autochtonous microbiota, the normal microbiota and the potentially pathogens acquired plays for the health’s host. In Topic II. “Description of bacteria” main genera of intestinal bacteria are discussed, focusing on ecology, physiology, metabolism and the resistance to antibiotics and others compounds alike. Furthermore this topic are applied to the bacterial taxonomy even to distinguish the pathogens s...