Most dengerous and interesting: Staphylococci, Streptococci, E. coli, Pseudomonas, Proteus, Salmonella, Shigella, Serratia, Klebsiella, Enterobacter, Campylobacter, Yersinia and Brucella.

To hitman

 

That question is too general to answer. Much depends on the species of bacteria, and much depends on the situation where the bacterium is transferred. For example : Staphylococcus aureus is found on most of us, and is pretty much harmless when it sits on our skin. But get it into an open wound in sufficient numbers, and it can be lethal.

 

There are also many strains of each. So multidrug resistant Staphylococcus aureus is much more dangerous than other strains.

 

Even something like Yersinia pestis (bubonic plague) varies enormously in how lethal it is, depending on where it is found. In skin, it leads to terrible sores, but most survive. In the lungs, it kills most of its victims.

In addition, (with the exception of E. coli you only provided the genera. There are a number of non-human pathogenous Yersinia species, for instance.