1) Avirulent 
not causing disease
Nonpathogenic: Incapable of causing disease. Nonpathogenic bacteria are harmless. By contrast, pathogenic bacteria can cause disease. For example, nonpathogenic E. coli are E. coli that are innocuous (like most E. coli) while pathogenic E. coli can make you sick. The word 'pathogenic' comes from two Greek roots: 'pathos' (disease) + 'genesis' (brin...