What it does
I'm not aware of "Infesting Spores" as an official Magic: The Gathering keyword or ability. It's possible this is a card name, a made-up term, or a misremembered ability—it doesn't correspond to any established keyword mechanic in the game.
You may be thinking of a few real things: Saprolings (the green/black creature tokens often made by "spore"-themed cards), the Spore counter mechanic from old Fungus creatures (which accumulate spores to make Saproling tokens), or Infect (a keyword where damage is dealt as -1/-1 counters and poison counters).
If you can share the exact card or where you saw "Infesting Spores," I'll gladly break down what it does, the common rules pitfalls, and how it plays in Commander. Without that, I don't want to invent rules that could mislead your game.
Iconic cards with Infesting Spores
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