The zombie bite. How does it work?

There used to be a ton of discussions on this topic back in the IMDb days and I'm curious after all this time what the current consensus is.

Here's what we know as in-universe fact from the show:
1. Everyone's infected. Everyone turns after they die.
2. A zombie bite is 100% fatal.

So, it follows that if you get bit by a zombie, you die and you turn. However, why do you die? There are two schools of thought on this:
1. The bite activates the latent infection, causing death, then turning.
2. The zombie mouth contains bacteria that causes a fatal infection, killing the victim, then turning.

As far as I know, the answer to this is not conclusively shown on-screen within the show.
Which do you believe and why?