**Preface**

This reprint deals with the study of the human microbiome and its influence on different pathologies, especially cancer, inflammation, intestinal damage, alterations in the normal gut integrity during *Clostridioides difficile* infections (CDIs), etc.

There are a variety of microorganisms in the human body, including fungi, bacteria, and viruses, that are usually harmless to the human body, and some can even protect our health by making vitamins, decomposing food, and regulating immunity. These microorganisms form a large group called the microbiome. The aim and purpose of this topic are related to the study of the changes in the human microbiome in the occurrence of many situations, such as CDIs, microbial translocation, pain, the spread of virulence and resistance genes among microbiomes, and so on.

The reasons for writing this work are correlated with the fact that our microbiota plays a vital role in our health. In fact, it protects us against pathogens, promotes the development of our immune system, and helps metabolize various compounds. Maintaining a balanced microbial ecosystem is essential for defending our health. This scientific study is mainly addressed to health professionals dealing with cancer, pain, and, in general, human health diseases other than metabolites secreted by the microbiome and their effects on patients with neuropathic diseases. Metabolomic technologies may provide critical information about the role of gut microbiome in cancer as well as molecular investigations, such as 16S rRNA sequencing, used in a study concerning the variability of human microbiome in the nasopharyngeal site in a population at different ages.

The authors involved in this Special Issue are the following: Piccioni A. Kneis B., Kunick F., Medakina I., Ganesan R., Candel S., Stupak A., Wronka D., Traina G., Dionisio F., Ustianowska K., and their respective collaborators.

I would like to acknowledge the support of my coworkers, Dania Al Ismail for drawing up the figure and Alessandra Oliva for the bibliography.

> **Maria Teresa Mascellino** *Editor*
