Cause of complaint from lycée? Endless one (1,4)
I believe the answer is:
e coli
'cause of complaint' is the definition.
(bacterium causing food poisoning)
'from lycee? endless one' is the wordplay.
'from' becomes 'e' (I've seen this in other clues).
'lycee?' becomes 'ecole' (I've seen this in another clue).
'endless' indicates the central letters.
'one' becomes 'I' (Roman numeral).
The middle letters of 'ecole' are 'col'.
'e'+'col'+'i'='E COLI'
(Other definitions for e coli that I've seen before include "Bug that causes food poisoning" , "Bacterium found in the gut" , "An infection found in food and water" , "cause of serious complaint" , "Gut bugs" .)