I'm not sure why you think "any one bacterium's mutation must become universal across the globe". That's a pretty strange takeaway in the presence of a mutation that is so advantageous it lets you become a predator and hunt other bacteria or run away from predators and gain a painfully obvious survivability benefit.

The takeaway should be "mutations that confer massive benefits can become universal across the globe even if they only happen once, no matter how unlikely they are", which is obvious and intuitive.