Nasty bug from priest keeping company (1,4)
I believe the answer is:
Here is my best explanation:
'nasty bug' is the definition.
(I've seen this before)
'priest keeping company' is the subsidiary indication.
'priest' becomes 'eli' (I've seen this before).
'keeping' indicates putting letters inside.
'company' becomes 'co' (abbreviation).
'eli' going around 'co' is 'ecoli'.
'from' is the link.
(Other definitions for e coli that I've seen before include "Gut bugs", "Bacterium found in the gut", "cause of ill-feeling", "Some types of this bacterium are toxic", "Bug that causes food poisoning", "Cause of internal problem", "cause of serious complaint", "Type of bacteria causing food poisoning", "Nasty bug" and "An infection found in food and water".)