How does the bacterial warfare work?
Say you have E. coli in your gut and you ingest some undercooked meat with new E. coli. It will do one of two things. It has to survive in your gut, which it has evolved to do, but also it has to find space in your gut. If there is already E. coli present, it cannot get it, so it produces a bacteriocin to destroy those already present and competing strains.