Asked that question and tested it a few times. Tepid 160F (71C) water like brewing temperature for coffee and tea kills virtually everything by three minutes steeping. That coincidentally, is the temperature for pasteurization, so don't drink day old tea that has been open to the air at room temperature. Leaving tea to set in water or worse, sweetened water for a day, more than 8 hours, will wake up (re-hydrate and re-activate) the spores of pond protozoa. Spores aren't killed easily and protozoan spores require 275F (135C) for one hour which is where total sterilization occurs nothing alive or having the potential for life survives. Pond protozoa are generally referred to as amoebas’ and hence the scourge amoebic dysentery.
It rarely seriously poisons somebody these days because the problem is very bad for the tea company and easily prevented by rinsing in sterile treated water. I’ve been to tea plantations all over the world, just by luck, and a lot depends on if the tea is for domestic use or export. I have had more than one night strapped to a toilet seat thanks to going native. A trick I learned quickly was to insist on boiling water. Most of us toss a cup in the microwave which has the unique ability to heat water well above boiling temperature, something with a small hazard potential if the water be suddenly agitated, but boiling the contents results in practical sterility.
A pre-biotic tea makes sense because it can contain digestive aiding compounds that go into the stomach. In effect, a probiotic tea is not going to deliver live cultures of anything, anywhere.
Enjoy the drink.
LL
