Bacterium (8)
'bacterium' is the definition.
(thesaurus)
This is the entire clue.
(Other definitions for bacillus that I've seen before include "A rod-like bacterium, can carry disease" , "Rod-shaped bacterium" , "Disease-causing organism" , "Rod-like bacterium, may cause disease" , "Type of bacterium" .)
'bacterium' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for germ that I've seen before include "tiny life form" , "Tiny organism that spreads disease" , "One causing disease" , "Seed; disease bringer" , "Micro-organism that causes disease" .)