Which of the following statements best describes the relationship between the size of the zone of inhibition and an organism's sensitivity to an antibiotic in the disk diffusion test?

• A. A large zone of inhibition indicates that the organism is sensitive to the antibiotic.
• B. The size of the zone of inhibition does not correlate with antibiotic sensitivity.
• C. A small zone of inhibition indicates high sensitivity to the antibiotic.
• D. A large zone of inhibition means the organism is resistant to the antibiotic.

Answer: (A)

Verified step by step guidance

1. Understand the principle of the disk diffusion test (also known as the Kirby-Bauer test), which is used to evaluate the effectiveness of an antibiotic against a specific microorganism by measuring the zone of inhibition around an antibiotic disk placed on an agar plate inoculated with the organism.
2. Recognize that the zone of inhibition is the clear area around the antibiotic disk where bacterial growth has been prevented due to the antibiotic's effect.
3. Know that the size of the zone of inhibition is inversely related to the organism's resistance and directly related to its sensitivity: a larger zone means the antibiotic is more effective at inhibiting growth, indicating higher sensitivity.
4. Recall that a small or no zone of inhibition suggests that the organism is resistant or less sensitive to the antibiotic, as the bacteria continue to grow close to the disk.
5. Conclude that among the given options, the statement 'A large zone of inhibition indicates that the organism is sensitive to the antibiotic' best describes the relationship between zone size and antibiotic sensitivity.