[xel02]

It is not nearly as so simple.

The majority of microbial species in the world cannot be cultured due to a lack of understanding in the nutritional requirements. This means microbiologists have a very difficult time studying them, one way of getting past this is studying the genetic makeup of a population.

However the best way to understand microbes is to grow them, a lot of bacteria are easy to grow (beef broth) others impossible.

Then there are ethical considerations in 'giving' people bacteria that are not well characterized.

It is a pretty well supported theory that exposure to bacteria is important for the development of the immune system, it is also pretty well accepted that the normal flora of humans is important in preventing infections.

How antibiotics, probiotics etc. affect humans are however much harder to characterize and understand.