The most common and most likely answer to this crossword clue is the 8 letter word SUPERBUG
I've seen this crossword clue in The Times
S
U
P
E
R
B
U
G
More clues leading to the result SUPERBUG
- Imposing university start to grow dangerous organism
- Energy drink first, then grub cooked for one not responding to treatment
- High copper tap that practitioner struggles to remove?
- Drunk urges pub to find resistant bacterium
- Pub user twisted bottom of leg, getting nasty strain
- Wonderful embrace of ‘Arry’s? It could kill you!
Buddy explains!

The straight part
We know that "one not responding to treatment" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case one not responding to treatment = superbug.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does SUPERBUG mean?
SUPERBUG noun- A strain of bacteria that is resistant to many antibiotics.
- Any pathogen resistant to many, even all, of the biocides or other agents used to treat similar pathogens.
- An invasive insect, Bemisia tabaci, that is a major pest of vegetable crops, both directly and as a virus vector.