In Kirby-Bauer disc diffusion testing, which indicates more sensitivity to the antibiotic?

In Kirby-Bauer disc diffusion testing, which indicates more sensitivity to the antibiotic?

• A. A larger zone of inhibition
• B. A smaller zone of inhibition
• C. Longer incubation time
• D. More discs used

Answer: (A)

A larger zone of inhibition indicates greater sensitivity to the antibiotic. In this test, antibiotic diffuses into the surrounding agar; if the organism is susceptible, its growth is stopped farther from the disk, creating a bigger clear area. A small or no zone means the organism is less inhibited or resistant. Incubation time or the number of discs aren’t direct measures of sensitivity under standard conditions, though they can affect results if not carefully controlled. Clinicians use the zone diameter, in comparison with standard breakpoints, to judge susceptibility.

A larger zone of inhibition indicates greater sensitivity to the antibiotic. In this test, antibiotic diffuses into the surrounding agar; if the organism is susceptible, its growth is stopped farther from the disk, creating a bigger clear area. A small or no zone means the organism is less inhibited or resistant. Incubation time or the number of discs aren’t direct measures of sensitivity under standard conditions, though they can affect results if not carefully controlled. Clinicians use the zone diameter, in comparison with standard breakpoints, to judge susceptibility.