The strain is very important and needs to be tailored for the body site.
The concept of a species in the microbial world is very different to the macro scale. Things are nowhere near as clear.
We are a species … Homo sapiens. We share approximately 99% of our genes with chimpanzees, our closest relatives.
For microbes though, there is a “core genome” for a species. This is the set of genes that is common to all strains of that species. Let’s take P. acnes as an example. There are more than 80 strains and the core genome makes up 88% of the genes. So if we were to apply that system to the macro world, we humans would be in the same species as chimpanzees … and cows … and mice.
Lactobacillus plantarum, a common probiotic microbe, has a core genome that makes up only 70% of its genes. This would put zebra fish and us in the same species. I don’t think that it would be fair to say that we occupy a similar ecological niche to zebra fish.
We have a lot to learn about the role of different microbial strains in the skin ecology but it is clear that the strain makes a big difference.
This can now be seen in the distribution of species across different body sites. As an example, there are some strains of S. epidermidis that occur only on the foot and as a rule different strains of S. epidermidis colonise different body sites on an individual. This is not necessarily true for P. acnes where the same strain seems to appear in multiple body sites on the same person.
This has consequences when we start adding probiotics to achieve a desired result. The strain is very important and needs to be tailored for the body site.