Final answer:
In a Kirby-Bauer disk diffusion test, there are three possible outcomes: susceptible, resistant, or intermediate, indicating how well a microorganism can grow in the presence of an antibiotic. Therefore, the most appropriate correct option is C.
Step-by-step explanation:
The Kirby-Bauer disk diffusion test is used to determine the susceptibility of a microorganism to various antimicrobial drugs. The correct answer to the question regarding the three possible outcomes for each antibiotic-microorganism pair in a Kirby-Bauer assay is C. Susceptible, resistant, or intermediate. In this context:
- Susceptible means that the microorganism cannot grow in the presence of the drug concentration represented by the zone of inhibition on the test plate.
- Resistant means the microorganism can grow despite the presence of the antibiotic, as indicated by a lack of significant zone of inhibition.
- Intermediate suggests that the microorganism exhibits some degree of sensitivity to the antibiotic, but this may not be sufficient for treatment effectiveness, as indicated by a smaller zone of inhibition that is neither clearly resistant nor susceptible according to standard charts.
During a Kirby-Bauer assay, if bacteria are susceptible, an area of clearing called the “zone of inhibition” will be seen surrounding the disks. The size of the zone of inhibition is measured and compared to a standardized chart to determine whether the bacterium is susceptible, resistant, or has an intermediate response to the antibiotic.