Exponential growth.
In a perfect world (for bacteria), a single E. coli bacterium could in the course of 24 hours divide enough times to create a colony more massive than the Earth. This is assuming that not a single bacteria would die in the course of that time and enough food was provided. Botulinium has a reproductive cycle fairly close to that of E. coli, so with the right equipment one vial could cause a lot of problems.