Pathogenic

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.