think systems theory of life, planet, rock, gas, organism, etc.
In a sense we aren’t distinct from the external world because there is no internal world to differentiate from. It’s imaginary - it exists only in our neurons, an abstraction to help us navigate reality, just impulses firing along various pathways in a brain.
They are still clearly seperate organisms, as a human does not require a particular bacterial cell, only that at least one is present in its proper place (the same as all the other cells in the human body). Thus, the "human organism" is an emergent organism from many cells, bacterial or not, acting and interacting non-deterministically. The bacterial cell by its existence allows for the existence of the larger organism.
A baby relies on adults to survive as well, but it is not biologically claimed that they are the same organism as the adults they rely on for survival.
We all require consumption of living and dead cells to survive as well. We do not claim organic-unification with these other organisms.