The human host and its microbial flora form a complex ecosystem whose balance is a striking example of reciprocal adaptation. Intestinal bacteria play a crucial part in the immune system's development. Resistance to colonisation by external pathogenic bacteria is due to the normal gut flora. Over 100 trillion symbiotic microbes live on and within humans, and they play a critical role in human health and disease. The human microbiota, particularly the gut microbiota, has been dubbed an "essential organ" since it contains 150 times the number of genes found in the human genome. The gut microbiota is engaged in basic human biological functions, such as modifying metabolic phenotype, regulating epithelial development, and impacting innate immunity, according to recent findings. In recent decades, a large body of research has strongly suggested that the human microbiota plays a critical role in human health and disease through a variety of methods. To begin with, the microbiota has the ability to improve energy extraction from meals, nutritional harvest, and appetite signalling.