[bee_rider]

Interesting point! I was thinking washed away germs remain in the gene pool so they aren’t selected out, but I guess the odds that they creep all the way back into the hospital to reproduce with the general population is quite low.

[SonOfLilit]

AIUI, a "gene pool" is much more of a thing with sexually reproducing organisms, where mutations either quickly spread across the gene pool, or they get diluted out, because you keep mixing everything together every generation. However, with bacteria, you just have both old and new bacteria each doing their thing.