Beach-closing bacteria (1,4)
I believe the answer is:
e coli
'beach-closing bacteria' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for e coli that I've seen before include "cause of ill-feeling" , "Type of bacteria causing food poisoning" , "Cause of internal problem" , "cause of illness" , "Bacterium found in the gut" .)