DING DING DING DING DING
WE HAVE A WINNER!!!
Lucky!
No, not the stomach. The stomach HELPS break down the food, but it is not a product of bacterial action, it is due peristaltic contractions, release of enzimes and a low pH (1-3).
So...
360!!
No, not the skin, but a good second guess. Considering the skin is the main physical barrier against micro-organisms it was a good guess.
Then...
Widget!!!
No, not the mouth, BUT a close call (even a better call than 360's since you were the last one to guess). The mouth is the FIRST place for digestion, involving enzimes and bacteria in the mouth to break down the food, but not enough bacteria.
Who is missing???
JANE!!!!!!!!!!!!!!!!!
YES!!! Common sense is better than anything. It is the intestine. In here, all the food that has been "attacked" in the previous processes of digestion will be digested (per se) in here. The gut flora is a main character, since the by-products of their consumption of our food will be absorbed by the intestinal cells.
We are a nice example of symbiosis