Also (sort of) the crux of one of my favorite horror manga, Biomeat: Nectar, which is about a genetically engineered animal that eats "garbage" (basically anyth

Also (sort of) the crux of one of my favorite horror manga, Biomeat: Nectar, which is about a genetically engineered animal that eats "garbage" (basically anything but metal, glass, and stone IIRC) and can be harvested for food, but escapes from the garbage plants and starts going after people. They're not microbes though, but more like nightmare fuel looking bugs about the size of a face, with the mouth on the bottom, and they reproduce via budding (like a hydra).