Could humanity end all life as we know it, even bacterial?
Yes, but I’m not telling you how for it would violate board rules.
Not a chance in Hell. We’ve found bacteria in core drillings miles down into the Earth’s crust. It pervades every nook and cranny on the Earth’s surface, down to the deepest parts of the ocean. We’d have to have the capability to completely melt the crust to be sure of destroying every last microbe.
Well, after the previous thread on the subject I was still unconvinced that it is beyond our thermonuclear capacity if we try really really hard to send the earth spiraling into the sun within our lifetimes. It’s farfetched but that would pretty much eliminate life on earth and the rest of life would have to float around space til it landed somewhere hospitable.
I’ve read enough science fiction to “know” that runaway nanotech can do the trick quite nicely. 
A very interesting recent thread on this very topic:
Could we actually Destroy The Earth?
See also this user manual:
How to destroy the Earth
It is theoretically possible to do this. No-one on Earth will be able to do this for another 20 years, if ever, though. And, I am not telling anyone how its done, because I want to get off this planet before any of you destroy it utterly.
Just out of curiosity, what board rules would it violate?
The main rule: Don’t be a jerk.
Telling people how to end all life on Earth! That’s not right!
I have heard (although I have no cite) that the probes we’ve sent to Mars might have carried bacteria along with them. If that’s the case, we’d have to destroy not only Earth but Mars as well. Of course, if you have the ability to destroy one planet, another shouldn’t be too difficult.
Assuming, as mentioned above, that we did not destroy Earth itself, then: no. Our best shot would just be another extinction event.
Um, presuming we’re setting this up from Earth, we would want to make sure we took out Mars first, then Earth. No, we’d probably forget and mess it all up. So I vote no.
Bacteria can live on Mars, even though there is no organic matter there?
I’m fairly sure it’s illegal in the United States to end all life as we know it, as such telling somebody how to do that violates board rules. 
Yes, it would involve the murder of some billions of human beings, of whom about 300,000,000 reside in the US, and would have to count as mass murder. (Though it would moot under US law, as there would be no judges or jurors left who could try you).
What would bacteria in the universe eat? Come to think of it, what does the bacteria in the core of the earth eat?
They feed on the corpses of the master race that lives on the inside of the earth.
The op said even bacteria, and I am not at all sure that we could do that. Even if we blew the Earth up entirley, some bacteria can survive in space.