It is important to maintain the species diversity and number balance in the intestinal microbiota. The microbiota members in the intestines are not actually our enemies; on the contrary, they are our friends, provided that the balance is maintained. Here, the disruption of the balance comes to the fore in terms of triggering medical pathologies; this situation can be determined with metagenome analyses, and the disrupted balance can be re-established with accurate formulations specific to the disease or person. APPLICATIONS THAT AIM TO ELIMINATE ALL BACTERIA IN THE INTESTINES ARE MEDICAL MURDER. There is no such application in medicine (except for bowel cleansing before surgery in the large intestine area).