Bacteria-ridden (6)
I believe the answer is:
septic
'bacteria-ridden' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for septic that I've seen before include "Infected with bacteria" , "Of wound, forming pus" , "Poisonous" , "Type of tank" , "Caused by putrefaction" .)