Final answer:
If there is no or a very small zone of inhibition around the disk in the Kirby-Bauer disk diffusion test, the organism is considered resistant to the drug.
Step-by-step explanation:
If there is no zone or a very small zone of inhibition around the disk in the Kirby-Bauer disk diffusion test, the organism is considered to be resistant to the drug. A zone of inhibition indicates that the drug is effective in inhibiting the growth of the organism, while a lack of zone or a small zone suggests that the organism is resistant to the drug.
The size of the zone of inhibition in the disk diffusion assay can vary depending on several factors, including drug concentration, drug solubility, rate of diffusion, and agar medium thickness. Therefore, the interpretation of the assay provides limited information on susceptibility and resistance to the drugs tested, and cannot be used to compare drug potencies or efficacy.