Why would those bacteria be adapted to infecting humans? The likelihood of a random bacterium being able to infect a human is very small unless there was evolutionary pressure for it to be able to.
Yeah, I think folks don't often realize how hostile an environment the human body can be to foreign invaders. Sure if you can sneak by the immune system, the human body is a microorganism paradise, but the immune systems of organisms are highly tuned to seek out and destroy foreign.
As everyone knows, there are secret nazi-bases below antarctica, so those are probably nazi-engineered bio weapons. :)