Food poisoning bacterium (8)
'food poisoning bacterium' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for salmonella that I've seen before include "Food poisoning bacterium" , "Bacteria causing food poisoning" , "stomach trouble" , "Nasty bug" , "Bacteria associated with food poisoning" .)
(Other definitions for listeria that I've seen before include "Hazard in badly kept food" , "Possible source of infection" , "Common pathogenic bacterium" , "disease" , "Is it real? (anag) -- kind of food poisoning" .)