What does a pathogenic bacterium have that nonpathogenic bacterium usually do have?

Answer 1

Using the Example From Above, He (or she) is Mostly Correct, but Everyone has "E. coli" In their Gut, if I Remember Correctly, Only One SEROTYPE of "E. coli" Leads to HUS, O157:H1.

Answer 2

Take E. coli as your example. The only thing that differentiates pathogenic E. coli from non-pathogenic E. coli is the location. In your intestines, E. coli is beneficial. When it is located elsewhere it is pathogenic.

Answer 3

pathogenic bacteria produce toxins (endotoxins or exotoxins) that nonpathogenic bacteria do not.