Antibiotic effectiveness measured by inhibition zone size

Steps:

• Examine the Petri dish for clear zones around each antibiotic disc where E. coli growth is inhibited.
• Compare the diameters of these zones of inhibition for discs A, B, C, and D.
• Identify the disc with the largest zone, indicating greatest bacterial killing and diffusion.
• Select disc C based on its superior zone size.

Why C is correct:

• The zone of inhibition diameter directly measures antibiotic potency; larger zones show stronger inhibition of bacterial growth per microbiology standards.

Why the others are wrong:

• A: Smallest zone indicates minimal bacterial killing.
• B: Moderate zone shows less effectiveness than C.
• D: Zone smaller than C, so reduced potency against E. coli.

Final answer: C