1. Which of the following is not a commonly used medium for antibiotic sensitivity testing? A. Mueller-Hinton agar B. MacConkey agar C. Blood agar D. Nutrient agar Answer: D. Nutrient agar Rationale: Nutrient agar is not typically used for antibiotic sensitivity testing because it lacks the standardized composition that is necessary for the Kirby-Bauer disk diffusion method. 2. When preparing a bacterial lawn for antibiotic sensitivity testing, it is important to ensure that: A. The bacterial suspension is too concentrated. B. The bacterial suspension is too dilute. C. The bacterial suspension is of the correct turbidity. D. The agar surface is dry. Answer: C. The bacterial suspension is of the correct turbidity. Rationale: The turbidity of the bacterial suspension must be standardized, often to a 0.5 McFarland standard, to ensure that the results of the antibiotic sensitivity test are reliable. 3. In the Kirby-Bauer disk diffusion method, what does a larger zone of inhibition indicate? A. Increased bacterial resistance to the antibiotic B. Decreased bacterial resistance to the antibiotic C. The antibiotic is ineffective D. The need for a higher concentration of antibiotic Answer: B. Decreased bacterial resistance to the antibiotic Rationale: A larger zone of inhibition around an antibiotic disk suggests that the bacteria are more sensitive to the antibiotic, indicating decreased resistance. 4. Which factor does not affect the outcome of an antibiotic sensitivity test? A. The thickness of the agar B. The concentration of the antibiotic in the disk