the article doesn't mention what concentrations the bacteria are found in because they are not in concentrations enough to do any harm to anyone but folks with limited to non-existent immune systems (of the boy in the plastic bubble type that is) who aren't going to be just running down to the Sev for a Big Gulp anyway. We live in a world of germs, our immune systems don't work if we aren't exposed to them regularly. If your immune system has nothing to attack, it will, just hanging out with all the rest of your inner workings, get bored and start looking for things to do It likes to fix things! "that *is* what it is there for after all! Why should it lay around doing nothing!" and it will go around fixing things regardless of their current working order. (kinda like those guys who, you will leave in the morning with them at the breakfast table with a coffee, and you will come home and they will have decided that the wall needed to be taken out, and part of the roof, because it was too dark in the kitchen, so the plumbing had to be re-routed through the neighbour's upper bedroom, and it turns out that the wall was a retaining wall, and you are renting. even if there was a perfectly good window blind they could have opened, directly to the left of the table,
*That* kind of fixing.
It is not surprising that the amount of auto-immune disorders have risen since we have become so 'germ-fearful', with anti-biotic this and antiseptic that, we only end up giving our immune systems an excuse for 'fixing' our own bodies, and end up killing of the least harmful germs, clearing the way for novel, more insidious, or double and triple resistant bacteria.
a few harmless bugs are good for the system.