I cannot find the reference, and only saw it on a recording. I have a very different attitude to many here - I spend only a few minutes a day in my rainfall shower, with hot water set above 135F and an exhaust fan. I don't have the energy to worry about that small an exposure, and considering I have been doing it this way for over 5 years post antibiotics without reinfection, I am feeling fairly safe.
In contrast, I spend hours each day outdoors, especially in my gardens and among my plants, so I take a few more precautions there.
But...I may be proven wrong in the future, and I do have a relatively high risk tolerance when it comes to balancing BE precautions against living my life. So this approach works for me, but others may not be comfortable with it.