By some estimates there are about one trillion species of bacteria on our planet. Fortunately, there are only about a thousand that cause disease and most of those are opportunistic pathogens (i.e., they only cause disease under unusual circumstances). That means that only 0.0000001% of bacterial species cause disease. The other 99.9999999% of bacterial species are neutral or even beneficial. But that tiny fraction that do cause disease can have devastating effects on humanity. For example, a bacterium called Yersinia pestis caused the Black Death that wiped out a quarter of the global population in the mid-1300s.
The following images are inspired by (but do not accurately depict) some of the genera of bacteria that cause disease in humans.
These illustrations were drawn using Stable Diffusion 2.1.