Abstract
Microorganisms are highly diverse and abundantly present in the natural environment. They typically enter the human body about 8 hours after birth and then reside on the surface of the skin and mucous membranes, such as those of the digestive, respiratory, and genital tracts. Each area of the body has differences in the composition and quantity of these microorganisms. Among these, the gastrointestinal tract hosts the richest microbiota, accounting for up to 90%. From there, they gradually increase in number and diversify in species within just 1-2 years.
The gut contains 100 trillion microbes, weighing approximately 1-2 kg. Bacteria make up 97%, archaea 0.1-0.2%, viruses 0.1%, and fungi 0.03-0.1%, with beneficial bacteria comprising 85% and harmful bacteria 15%. The number of microbes is ten times greater than the number of living cells in an adult human body, and their genetic material totals over 3 million genes, which is 150 times the number of human genes.