Earth bacteria traveling through space

There is indeed Earth bacteria careening through space. What would happen if...

1) Chances of coming anywhere near another solar system - slim
2) Chances of approaching a life sustaining (or life sustainable) planet - slimmer
3) Chances of contacting that planet in a manner that does not destroy the bacteria and its carrier - slimmest

I don't think we have to worry about wiping out an alien population with our colds... which reminds me... who watches Battlestar Galactica on TV? Remember the cold the Cylons got? What ever happened to that cold anyway?

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