Question 1

Which of the following best describes the purpose of the clear zones surrounding some antibiotic disks in the image provided?

Accepted Answer

They indicate areas where the antibiotic has killed or inhibited bacterial growth, known as zones of inhibition.

Question 2

If an antibiotic disk shows no clear zone around it on a bacterial lawn, what does this indicate about the bacteria's response to that antibiotic?

Accepted Answer

The bacteria are resistant to the antibiotic.

Question 3

Why can't you directly compare the size of the zones of inhibition for different antibiotics on the same organism to determine which antibiotic is most effective?

Accepted Answer

Because the rate of diffusion depends on the molecular weight and solubility of each antibiotic, not just its effectiveness.

Question 4

What is the correct term for the method shown in the image, where antibiotic disks are placed on a bacterial lawn to test for sensitivity?

Accepted Answer

Disk diffusion assay (Kirby-Bauer test)

Question 5

If a new antibiotic with a high molecular weight is tested using the disk diffusion method, what would you expect regarding its zone of inhibition compared to a low molecular weight antibiotic, assuming equal effectiveness?

Accepted Answer

The high molecular weight antibiotic would likely have a smaller zone of inhibition due to slower diffusion.

Question 6

What is the primary reason for using Mueller-Hinton agar in the disk diffusion (Kirby-Bauer) test?

Accepted Answer

It allows for consistent diffusion of antibiotics and reliable measurement of inhibition zones.

Question 7

A student observes that the zone of inhibition around the penicillin (P) disk is absent, but there is a large zone around the chloramphenicol (C) disk. What can be concluded about the organism's sensitivity?

Accepted Answer

The organism is resistant to penicillin and sensitive to chloramphenicol.

Question 8

Which equation best describes the relationship between the concentration of antibiotic and the distance from the disk in a disk diffusion assay?

Accepted Answer

The concentration decreases logarithmically with distance: $$C = C_0$ \cdot e$$^{-kd}$$

Question 9

If you wanted to determine the minimum inhibitory concentration (MIC) of an antibiotic, which method would be more appropriate than the disk diffusion assay?

Accepted Answer

Broth dilution method

Question 10

In the disk diffusion assay, what would be the effect of increasing the initial concentration of bacteria plated on the agar?

Accepted Answer

Zones of inhibition would likely become smaller due to increased bacterial density.

Microbiology Practical Review: Media, Indicators, and Antimicrobial Susceptibility

Study Guide - Practice Questions

Study Guide - Flashcards