Pathogenic
Causing disease or capable of doing it.
Pathogenic bacteria are disease-causing bacteria.
For example, pathogenic E. coli are E.
Coli that are not innocuous (like most E.
Coli) but can make a person ill and even kill them.
The word 'pathogenic' comes from two Greek roots: 'pathos' (disease) + 'genesis' (bringing into being) = literally, bringing disease into being.