A source of bacteria in European circus performer (7)
I believe the answer is:
acrobat
'circus performer' is the definition.
(type of performing gymnast)
'a source of bacteria in european' is the wordplay.
'source of' says to take the initial letters.
'in' is an insertion indicator.
'european' becomes 'croat' (person from Croatia).
The initial letter of 'bacteria' is 'b'.
'b' going inside 'croat' is 'crobat'.
'a'+'crobat'='ACROBAT'
(Other definitions for acrobat that I've seen before include "One appearing head over heels" , "Agile entertainer" , "Athletic type" , "Boat car (anag.)" , "Gymnastic entertainer" .)