Contaminated with bacteria (6)
I believe the answer is:
septic
'contaminated with bacteria' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for septic that I've seen before include "Caused by putrefaction" , "Of wound, infected and pus-filled" , "Type of tank" , "Of wound, infected with pus" , "Relating to putrefaction" .)