*Review* **Gut Microbiota and** *Clostridium difficile***: What We Know and the New Frontiers**

**Andrea Piccioni 1, Federico Rosa 2, Federica Manca 2, Giulia Pignataro 1, Christian Zanza 3, Gabriele Savioli 4, Marcello Covino 1,2, Veronica Ojetti 2, Antonio Gasbarrini 1,2, Francesco Franceschi 1,2 and Marcello Candelli 1,\***


**Abstract:** Our digestive system, particularly our intestines, harbors a vast amount of microorganisms, whose genetic makeup is referred to as the microbiome. *Clostridium difficile* is a spore-forming Gram-positive bacterium, which can cause an infection whose symptoms range from asymptomatic colonization to fearsome complications such as the onset of toxic megacolon. The relationship between gut microbiota and *Clostridium difficile* infection has been studied from different perspectives. One of the proposed strategies is to be able to specifically identify which types of microbiota alterations are most at risk for the onset of CDI. In this article, we understood once again how crucial the role of the human microbiota is in health and especially how crucial it becomes, in the case of its alteration, for the individual's disease. *Clostridium difficile* infection is an emblematic example of how a normal and physiological composition of the human microbiome can play a very important role in immune defense against such a fearsome disease.

**Keywords:** gut microbiota; *Clostridium difficile* infection; microbiome
