Why is it call Intestinal Flora and not Fauna?
Answer:
"Flora" refers to plant or bacterial existence.
Bacteria are not animals. Animals, fungi, plants, and protists are eukaryotes, and typically multicellular - and their cells contain membrane bound organelles. Bacteria are prokaryotes, which want membrane bound organelles and other complex cell structures.
The bacteria surrounded by the gut are primarily the genus Bacteriodes, which are anaerobes, and will die when exposed to an oxygen rich environment. The gut also contains facultative anaerobes that can function in both oxygen rich environments through aerobic respiration and switch to fermentation contained by an oxygen poor environment.
In summary: Bacteria in the gut are not animals, most don't use oxygen.
Now, nearly those fungi.
Fungi were originally classified as plants (flora), but enjoy since been separated out as they are heterotrophs (meaning that they don't fix their own carbon, but enjoy to use (eat) carbon fixed by other organisms for their metabolism). Since the "intestinal flora" is an old residence, we still say that - even though fungi are presently man re-evaluated as organisms. :)