Multiple Choice
Based on the image, which drug do you think would be most effective at inhibiting the bacteria on the agar?
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28. Antimicrobial Drugs
Tests to Guide Antimicrobial Use
Multiple Choice
What can an E-test tell you that a standard Kirby-Bauer test cannot?
A
An E-test can tell you whether a particular antibiotic is effective against a particular bacterium.
B
An E-test can tell you the MIC.
C
An E-test can tell you the MBC.
D
An E-test can tell you both the MIC & the MBC.
Verified step by step guidance1
Step 1: Understand the Kirby-Bauer test, which is a disk diffusion method used to determine if a bacterium is susceptible or resistant to an antibiotic by measuring the zone of inhibition around antibiotic disks on an agar plate.
Step 2: Recognize that the Kirby-Bauer test provides qualitative results (susceptible, intermediate, or resistant) but does not give a precise quantitative value of antibiotic concentration needed to inhibit bacterial growth.
Step 3: Learn that the E-test (Epsilometer test) uses a strip with a gradient of antibiotic concentrations, allowing determination of the Minimum Inhibitory Concentration (MIC), which is the lowest concentration of antibiotic that inhibits visible bacterial growth.
Step 4: Note that the MIC is a quantitative value that helps clinicians choose the appropriate antibiotic dosage, which the Kirby-Bauer test cannot provide.
Step 5: Understand that while the E-test can determine the MIC, it does not directly measure the Minimum Bactericidal Concentration (MBC), which requires additional testing to find the lowest concentration that kills bacteria.
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