In a Kirby-Bauer susceptibility test, the presence of a zone of inhibition around disks containing antimicrobial agents indicates __________ .


a. that the microbe does not grow in the presence of the agents
b. that the microbe grows well in the presence of the agents
c. the smallest amount of the agent that will inhibit the growth of the microbe
d. the minimum amount of an agent that kills the microbe in question

Verified step by step guidance

1. Understand the purpose of the Kirby-Bauer test: It is used to determine the susceptibility of a microorganism to various antimicrobial agents.
2. Recognize that the test involves placing disks containing antimicrobial agents on an agar plate inoculated with the microbe.
3. Observe the zone of inhibition, which is the clear area around the disk where the microbe does not grow.
4. Interpret the presence of a zone of inhibition: It indicates that the microbe is susceptible to the antimicrobial agent, meaning it does not grow in its presence.
5. Consider the options given: The correct interpretation aligns with option a, as the zone of inhibition shows that the microbe does not grow in the presence of the agents.

Key Concepts

Kirby-Bauer Test

The Kirby-Bauer test is a standardized method used to determine the susceptibility of bacteria to various antimicrobial agents. In this test, paper disks impregnated with specific antibiotics are placed on an agar plate inoculated with the bacteria. After incubation, the effectiveness of the antibiotics is assessed by measuring the zones of inhibition, which indicate how well the antimicrobial agents can prevent bacterial growth.

Zone of Inhibition

The zone of inhibition is the clear area surrounding an antibiotic disk on an agar plate where bacterial growth has been prevented. The size of this zone is directly related to the effectiveness of the antimicrobial agent against the tested bacteria. A larger zone indicates greater susceptibility, while a smaller or absent zone suggests resistance to the antibiotic.

Antimicrobial Susceptibility

Antimicrobial susceptibility refers to the sensitivity of bacteria to specific antimicrobial agents. It is crucial for determining the appropriate treatment for infections. In the context of the Kirby-Bauer test, the presence of a zone of inhibition signifies that the bacteria are susceptible to the antimicrobial agent, meaning they do not grow in its presence, which is essential for effective clinical decision-making.