Bifidobacterium spp. such as Bifidobacterium bifidum, Bifidobacterium breve and Bifidobacterium longum are the examples of non-pathogenic Gram positive bacteria residing in human gut. Please take a look at the following references.
Article Bifidobacteria and Their Role as Members of the Human Gut Microbiota
Article Bifidobacterium bifidum as an example of a specialized human...