The mucus that covers it comes in two layers: a dense inner one that sits directly on top of the epithelial cells, and a loose outer one beyond that. The outer layer is full of phages, but it’s also a place where microbes can anchor themselves and build thriving communities. They abound here. By comparison, very few of them exist in the dense inner layer. That’s because the epithelial cells liberally spray this zone with antimicrobial peptides (AMPs) – small molecular bullets that take out any encroaching microbes.
