Basically they built on [a] germ free mouse model and introduced a defined set of cultured microbes that came from humans. And then they stage[d] a phage attack on the system and monitored the response of the community to the phage attack.
They (of course) also did a control - in this case with heat killed phage. And they compared what happened to the live phage. I love this concept as they are able to control the microbial community and then test dynamics of how specific phage affect that community inside a living host.