[katieHaylor (OP)]

Graham says:

I read a book called Gut which made me aware of the trillions of organisms in the human body, but how do they get there?

Can you help?

[axscientist]

According to gutmicrobiotaforhealth, "Colonization of the gut by the human microbiome was thought to begin at birth, but some scientists have reported that a mother-to-child transfer of commensal bacteria through the placental barrier may occur. The maternal oral microbiome has been suggested as the source of the first bacteria that colonize infants."

So we can be born with it and we can develop it as we grow.

[Petrochemicals]

I believe the microbiome is accumulated through the environment. Heavy antibiotics will wipe out the gut bacteria, to the point that doctors will prescribe gut bacteria drinks (many brands are Avaliable). Other sources are fresh fruit vetetables, the environment in general.

[evan_au]

The maternal oral microbiome has been suggested as the source of the first bacteria that colonize infants.

The maternal vaginal and fecal microbiome would be an even earlier source.
- But the nursing staff try to clean this out of the newborn's mouth
- Babies born by caesarian miss out on both of these sources, and caesarian are thought to have slightly different microbiomes.
- Some people have taken to oral seeding of vaginal fluids in babies born via caesarian
See: https://en.wikipedia.org/wiki/Vaginal_seeding
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6085361/

It is thought that the digestive system of newborns are less aggressive than in older children, perhaps allowing microbes to enter and colonize the gut.

But children pick up bacteria all the time. Scientists analyzing gut bacteria claim that they can determine whether the family has a dog.