I don't repopulate after enemas, but I do take (high dose) probiotics and prebiotics daily. I don't think they are implanting - probably because my colon is toxic.
I also take Emergen-C (for electrolytes).
parasites is a possibility (albeit a remote one). Sometimes I get these floating seed like things in my enemas, and I'm pretty sure they are not foodstuff. They look like Watermelon seeds except they are flat and yellow (not black).
On examination they don't look like anything living, but I can't be 100% sure.