Stalin's enforcer concealed routine bugs (8)

I believe the answer is:

bacteria

I'm a little stuck... Click here to teach me more about this clue!

'bugs' is the definition.
(I've seen this before)

'stalin's enforcer concealed routine' is the wordplay.
'stalin's enforcer' becomes 'beria' (I can't justify this - if you can you should give a lot more credence to this answer).
'concealed' is an insertion indicator.
'routine' becomes 'act' (synonyms).
'beria' enclosing 'act' is 'BACTERIA'.

Can you help me to learn more?

(Other definitions for bacteria that I've seen before include "Microscopic organisms, may carry diseases" , "Care a bit about sources of diseases" , "Agents of infection" , "Tiny organisms, may be good or bad" , "could make you feel bad" .)

I've seen this clue in The Guardian.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.