You performed a Kirby-Bauer test with three antibiotics: X, Y, and Z. Measured inhibition zones are X = 22 mm, Y = 17 mm, Z = 9 mm. Clinical breakpoints from the reference state: X susceptible ≥ 20 mm; Y susceptible ≥ 18 mm and intermediate 15–17 mm; Z susceptible ≥ 15 mm. How should each antibiotic be classified and how should they be comparatively ranked for empirical selection?

• A. X is resistant because 22 mm is only marginally above the breakpoint and therefore unreliable, Y is susceptible because 17 mm indicates likely clinical success in most tissues even though it sits at the lower limit, and Z is intermediate; rank: Y > X > Z.
• B. X is intermediate and should be avoided for systemic infections because its zone is only 22 mm, Y is resistant as it is below the susceptible cutoff, and Z is susceptible contrary to the reference because clinical effectiveness often occurs even when zones are small; rank: Z > X > Y.
• C. All three are resistant because the presence of any zone smaller than 25 mm implies insufficient diffusion and therefore clinical failure, so none should be used and therapy should rely entirely on combination empiric therapy pending molecular diagnostics.
• D. X is susceptible (recommended), Y is intermediate (may work at higher doses or if concentrated at infection site), Z is resistant (not recommended); rank: X > Y > Z.

Answer: (D)