Impact of the gut microbiota, prebiotics, and probiotics on human health and disease

Abstract

M ore than 100 trillion (10 14 ) microbes inhabit the hu- man gastrointestinal (GI) tract, and the total number of genes derived from these microbes exceeds that of the human genome by at least 100-fold.In the stomach of healthy human adults, a relatively low number of bacteria can be found, approximately 10 4 colony forming units (CFU) per milliliter of gastric content, which mainly correspond to bacilli, catenabacteria, enterococci, and lactobacilli [Figure 1].[1] Helicobacter pylori is also present in the stomach of more than half of the human population.[2] The first part of the small intestine, the duodenum, is acidic (pH 4-5) and a relatively large number of bacteria (10 2 -10 4 CFU/ml) are found in this section.[3] Lactobacilli, streptococci, veillonellae, staphylococci, actinobacilli, and yeasts are the most prominent organisms in the duodenum and jejunum.[4] The GI microbiota changes markedly from the duodenum to the ileum due to an increase in pH and reduction of oxidation-reduction potentials, leading to an increase of the bacterial load which can reach up to 10 6 -10 8 Special EditionRecent studies have revealed that the gut microbiota regulates many physiological functions, ranging from energy regulation and cognitive processes to toxin neutralization and immunity against pathogens.Accordingly, alterations in the composition of the gut microbiota have been shown to contribute to the development of various chronic diseases.The main objectives of this review are to present recent breakthroughs in the study of the gut microbiota and show that intestinal bacteria play a critical role in the development of different disease conditions, including obesity, fatty liver disease, and lung infection.We also highlight the potential application of prebiotics and probiotics in maintaining optimal health and treating chronic inflammatory and immunity-related diseases.