14 Combating Microbes

Procedure:

• Please check out Monday’s recording where I explained the antibiogram and showed results. I explained what to do this week and we had some other discussions.
• So for combating microbes you will do first the virtual lab Virtual Activity: Kirby-Bauer Antimicrobial Susceptibility TestLinks to an external site.
• Make sure you click through the different organisms that are available for testing and pick 3 of the antibiotics and compare the results. Think about how Gram+ and Gram- organism react differently.

Steps for Kirby-Bauer method of antimicrobial susceptibility testing

1. From the main menu, click “Start” to begin the exercise.

2. Using the virtual ruler (the mouse), measure the zone of inhibition – the diameter of the clear zone (no bacterial growth) around each antibiotic disc – in millimeters. This is the zone in which bacterial growth has been inhibited by the antibiotic in the disc.

3. Compare the zone sizes to the values in the Table of Interpretive Standards next to the plate.

4. Click on the box corresponding to the appropriate result: R (resistant), I (intermediate), or S (susceptible).

5. Continue for each disc until the entire plate has been scored and the table is complete. 6. Click on “Restart” to start over. (note: the exercise will restart with a different organism.)

Results:

The organism that is plated in the virtual lab is Escherichia coli. The results show that the most effective antibiotics for inhibiting E.coli are Streptomycin, Tobramycin, Trimethoprim Sulfa, Ciprofloxacin, Chloramphenicol, and Cephalothin. This is because they have the greatest zones of inhibition.

The Kirby-Bauer Antimicrobial Susceptibility Test is an essential tool for evaluating the effectiveness of antibiotics against specific bacterial pathogens. It helps clinicians select the most appropriate antibiotic for treating infections, ensuring targeted and effective therapy. By identifying antibiotics to which bacteria are resistant, the test minimizes the use of ineffective treatments, thereby reducing the risk of antibiotic resistance. It also provides timely information critical for initiating proper treatment and improving patient outcomes. Additionally, the test is valuable for monitoring resistance trends in public health, allowing researchers to track and respond to the emergence of resistant strains. Its simplicity, cost-effectiveness, and accessibility make it a widely used method in clinical and research settings, supporting infection control and antimicrobial stewardship efforts.