JDREAM. Journal of interDisciplinary REsearch Applied to Medicine JDREAM (2021), v. 5 i. 1, 7-10 ISSN 2532-7518 DOI 10.1285/i25327518v5i1p7 http://siba-ese.unisalento.it, © 2021 Università del Salento 7 The bidirectional interaction between our gut flora and drugs Luana Conte 1, 2 , Cosimo Caldararo 2 , Roberto Lupo 3 1 Laboratory of Interdisciplinary Research Applied to Medicine (DReAM), University of Salento and ASL (Local Health Authority) Lecce, Italy 2 University of Bari, Bari, Italy 3 "San Giuseppe da Copertino" Hospital, ASL (Local Health Authority) Lecce, Italy Corresponding author: Luana Conte luana.conte@unisalento.it Abstract The term "pharmacogenetics" refers to the study of individual genetic variations that give rise to different re- sponses to the intake of a drug. Recently, however, it has begun to think that an important role in this sense can also be played by our microbiota. The interaction between our gut microbial flora and drugs is actually bidirec- tional: evidence has accumulated that some drugs, in addition to classical antibiotics, have a strong impact on the composition of the microbiota. Keywords: microbiota, drugs 1. Introduction The term microbiota refers to the millions of billions of microorganisms (bacteria of thou- sands of different species, Archaea, viruses, and fungi that crowd our organism). These mi- crobes live on the skin, in the mucous mem- branes of the mouth, in the respiratory tract, but a particularly important role is played by the intestinal component, a diverse and dense mi- crobial community, unparalleled in other bodily habitats. At birth, the digestive tract is almost sterile: the intestinal microbiota is transferred from the mother to the child during childbirth, when it occurs naturally, and this process of colonization continues during the first days of life, with different species depending on wheth- er the infant is artificially or breastfed. It then undergoes a prolonged period of postnatal de- velopment, during which it is influenced by contact with external agents such as foods, metals, and toxic substances. It is estimated that the intestinal bacterial herit- age of an adult is composed of over one hun- dred trillion cells, most of which belong to six bacterial phyla: Firmicutes, Bacteroidetes, Actinobac- teria, Proteobacteria, Fusobacteria and Verrucomicro- bia. They perform functions essential to our health, such as the breakdown of plant polysac- charides - fibers - indigestible by the host, the detoxification of xenobiotics, substances for- eign to the body, the suppression of the growth of harmful microorganisms by competitive ex- clusion and the development of the host im- mune system, the biosynthesis of essential vit- amins and amino acids. For example, our or- ganism is unable to produce vitamin K, which is essential for the proper synthesis of coagula- tion factors, and uses, in addition to the diet, that which is produced by some bacteria of our resident intestinal microbial flora. The healthy pulmonary microbiota contains many commensal bacteria derived from the up- per respiratory tract, mainly belonging to the phylum Bacteroidetes, especially the genus Prevotel- la, and the phylum Firmicutes, especially Veilonel- la and Streptococcus (Dickson et al. 2015). Its composition is determined by numerous factors and anatomo-clinical circumstances: a) dis- placement of bacteria from the upper airways by passive migration, b) gastroesophageal mi- cro-aspiration from the digestive tract c) sapro- phytic anti-infective activity by the innate and adaptive defenses of the healthy lung, d) by