Former European bacteriologist (7)
I believe the answer is:
pasteur
'bacteriologist' is the definition.
(I've seen this before)
'former european' is the wordplay.
'former' becomes 'past' (similar in meaning).
'european' becomes 'Eur' (abbreviation for European).
'past'+'eur'='PASTEUR'
(Other definitions for pasteur that I've seen before include "Louis -, nineteenth century French chemist" , "He developed the partial sterilization of milk" , "Famous bacteriologist" , "Louis --, French bacteriologist" , "French chemist and biologist, d. 1895" .)