Bacterial resistance indicated by shrinking inhibition zones

Steps:

• Review zone diameter changes in the table over 5 days.
• Type 1 decreases from 24.1 mm to 14.3 mm, showing emerging resistant bacteria.
• Type 2 decreases from 18.6 mm to 6.3 mm, showing emerging resistant bacteria.
• Type 3 decreases from 17.9 mm to 10.9 mm, showing emerging resistant bacteria.
• Types 4 and 5 remain stable near 20 mm, showing no resistance development.

Why B is correct:

• Decreasing zones indicate resistant bacteria growing into the cleared area (per standard antibiotic sensitivity testing, where shrinking zones signal resistance emergence before reaching <1.0 mm threshold).

Why the others are wrong:

• A: Types 4 and 5 do not decrease, so not all become resistant.
• C: Bacteria types do not "treat" others; this misinterprets the experiment.
• D: Data shows type 5 remains sensitive over 5 days, but cannot confirm "never."

Final answer: B