In Pretear, Leafe is what makes living things be alive. However, when demons leach it from things, the leaching spreads over not only living things but also inanimate objects like bicycles. How does that work?
It's been far too long since I watched this series, but if you don't mind breaking the first law of anime ("real world physics don't apply to anime"), then this might be a decent explanation.
Bacteria are tiny lifeforms too small to see with the naked eye, and they're everywhere: floating through the air, on every surface you touch, all over your body, all in your body. Anywhere life can exist, bacteria are there. That's probably what the Leafe was flowing through.