Bacteria is just a type of cell, it doesn't have a physical size to it that can actually be seen by the naked eye! The colour comes from the liver bile!
Stomach acid is capable of destroying anything! Remember we grow stronger with age, a grown man or woman can easily disintegrate a whole meal. The stomach muscles have to flex constantly to keep churning the food around. I was referring to the acid in a beaker that was just simply left by itself on a table. That is not our body, and we have also enzymes that are made to help speed up the process.
How else does the chyme go through the tiny strainers of the intestinal wall? it needs to be fine enough to go in. If we release more food than we're taking in, we won't be growing the way we're supposed to. We're SUPPOSED to get bigger and fatter when we eat food! Bodybuilders eat well over 3 meals a day and the key is to burn it all off with a fast metabolism! We're consuming machines, that simply take in everything around us. ANY food group if looks yummy enough should contribute to your body size. It's not fair that you only get HALF the consequences of eating :D.
EDIT: We also have a lining inside our stomach that prevents the acid from eating away at our stomach wall. God put us on this planet to survive and be happy, surely the system works