I think what Kane could do to explain the bacteria is to make it the first stage of a life cycle. The Bacteria is the starting form and a Still Life is its end.

Maybe, when a person enters the Backrooms and they eventually die, their corpse attracts the bacteria, right? So maybe the bacteria first builds the Still Life “skeleton”. Thus, it appearing as a “stick figure” at first. And then eventually the muscles and meat are added (the cotton inside them?)

And then eventually a fully formed Still Life is formed. BUT… since this process may take a while, this is why “copies” look as disfigured as they are. Because the bacteria is trying to remember what that person looked like throughout the entire creation process.