**2.3 Evolution and resilience**

Even though a tiny amount of pathogens via maternal blood could produce a first microbiome at delivery, fetuses are assumed to be sterile during pregnancy [33]. Viruses out from the mother and the surroundings infiltrate the newborn's intestines almost immediately. The microbiota's makeup is influenced by cesarean delivery, antimicrobial therapy, nutrition, and ambient hygiene [34]. Bacterial flora in your intestines is extremely stable throughout maturity, shifting just a little around a core of stable colonizers. The gut physiology and nutrition of humans alter as they get older [35]. Temporary changes, however, may occur as a result of dietary factors or antibiotic treatments. Quick medication with only a solitary prescription with antibiotic therapy, such instance, alters the intestinal flora lasting up to 4 days until returning to its previous state [36]. In addition, some bacteria might take months of rehab after treatment, resulting in a loss of diversity after multiple medication exposures [37]. Dietary modifications have a similar effect on the makeup of intestinal flora. Food provides nutrients to the host as well as the microbiota, whose bacteria may be favored or injured by dietary substrates. As a result, according to one study, changes in diet in mice could responsible for 57% of the overall point mutation in gut microbes, while gene variants accounted for only 12% [38].

So far, the gutMEGA database has collected the gut microbes of 6457 taxa [39]. Firmicutes, Bacteroides, Proteus, Actinomycetes, Fusobacteria, and Verrucomicrobia comprise the bulk of the human gut microbiota [40]. Varied gut flora is ultimately beneficial; nevertheless, a lack of choice in the gut microbiome may lead to disorders such as obesity [23]. Another feature of gut health microorganisms is a delicate balance, which refers to the gut microbiota's capacity to resist perturbation and return to health, such as following antimicrobial therapy [41].
