The ruling in our PFS today was that if the enemy has no SR, the infusion will not work. Main argument was the clause of needing to hit AND penetrate SR, and since there's no rule stating a creature without SR listed has SR=0, there's no SR to penetrate, and thus the infusion does nothing. It might not make logical sense, but it doesn't have to. That's just how it is. It's only a LV1 infusion, so it's not gonna be terribly useful anyway.