Interpreting Bacterial Resistance via Inhibition Zones

Steps:

• Identify N as the control with no antibiotic, showing unrestricted bacterial growth for comparison.
• For bacteria P, observe a clear zone around antibiotic X disc (indicating sensitivity) but no zone around Y (indicating resistance to Y).
• For bacteria R, observe no clear zones around either X or Y discs, indicating resistance to both antibiotics.
• Conclude resistance in R likely results from a genetic mutation allowing growth despite antibiotics.

Why D is correct:

• In antibiotic sensitivity tests, lack of inhibition zones around both X and Y discs for R demonstrates resistance to both, typically due to a mutation conferring this trait.

Why the others are wrong:

• A: P shows sensitivity to X (clear zone), so not resistant to both.
• B: P's resistance is to Y only, not due to a specified mutation; R shows broader resistance.
• C: N is a general control without any antibiotic, not specific to Y's absence for R.

Final answer: D