The gut microbiota as a biomarker for realistic exposures to pesticides: A critical consideration

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In mammals, the gut microbiota (GM) exerts important physiological functions. The abundance of bacterial, fungal and protozoan microorganisms colonizing the gut determines the nutrients that will be taken from the diet, the production and absorption rates of vitamins, and the ability of various metabolic pathways to activate or detoxify xenobiotics. Several studies have allowed characterizing the plastic changes occurring in the GM from birth to adulthood, the extent of intra- and inter-individual variability, and the influence of the housing/caging conditions and diet on the microbiome composition of the gut. The structural and functional integrity of the GM has been increasingly proposed as a biological determinant of the susceptibility to developmental disorders. More recently, some research articles have shown some potentiality of this microbial assembly as a possible biomarker for environmentally relevant exposure to chemical hazards. In this review, we performed a comprehensive survey on GM studies in rats and mice exposed to insecticides, herbicides and fungicides, exhaustively considering the influence of several biological and experimental factors, including the animal's age, diet, breeding type, housing and caging conditions and sampling protocol, on the results observed. For pesticides for which no reliable biomarker has yet been developed in mammals, the utility and predictive power of microbiome assays will strongly depend on the rigorous selection and application of the study design features.