*Review* **What Pediatricians Should Know before Studying Gut Microbiota**

**Lorenzo Drago 1,2,\*, Simona Panelli 2, Claudio Bandi 2,3, Gianvincenzo Zuccotti 4, Matteo Perini 2 and Enza D'Auria 4**


Received: 2 July 2019; Accepted: 9 August 2019; Published: 12 August 2019

**Abstract:** Billions of microorganisms, or "microbiota", inhabit the gu<sup>t</sup> and a ffect its homeostasis, influencing, and sometimes causing if altered, a multitude of diseases. The genomes of the microbes that form the gu<sup>t</sup> ecosystem should be summed to the human genome to form the hologenome due to their influence on human physiology; hence the term "microbiome" is commonly used to refer to the genetic make-up and gene–gene interactions of microbes. This review attempts to provide insight into this recently discovered vital organ of the human body, which has ye<sup>t</sup> to be fully explored. We herein discuss the rhythm and shaping of the microbiome at birth and during the first years leading up to adolescence. Furthermore, important issues to consider for conducting a reliable microbiome study including study design, inclusion/exclusion criteria, sample collection, storage, and variability of di fferent sampling methods as well as the basic terminology of molecular approaches, data analysis, and clinical interpretation of results are addressed. This basic knowledge aims to provide the pediatricians with a key tool to avoid data dispersion and pitfalls during child microbiota study.

**Keywords:** gu<sup>t</sup> microbiota; microbiome; maternal–fetal interface; newborn; child; pediatric disease; dysbiosis
