4. Trent is a medical technician in a hospital microbiology laboratory where one

Question

4. Trent is a medical technician in a hospital microbiology laboratory where one of his duties is to prepare and read the results of Disk Diffusion (Kirby-Bauer) tests. Trent needs to do a Disk Diffusion (Kirby-Bauer) test on a pure culture of a bacterial specimen isolated from a young child's extremely red, swollen and pus-filled tonsils. Trent dilutes the bacterial specimen so that it is comparable to a 0.5 McFarland standard but then decides to go to lunch and run an errand and places the diluted sample in the 37°C incubator. When he returns 2 hours later, Trent takes the sample from the incubator and uses it to inoculate his Disk Diffusion (Kirby-Bauer) plate. Fortunately, Trent's supervisor has seen what he has done and tells him that for all Disk Diffusion (Kirby-Bauer) tests diluted bacterial samples must be used within 20 minutes. Why is this so important? If the Disk Diffusion (Kirby-Bauer) test Trent prepared was used what effect could it have on the results? [2 pts]

Explanation / Answer

The diluted bacterial samples should be used within 20 minutes because if left beyond that time, it will lead to multiplication of bacterial cells. This will increase the concentration of bacteria in the diluted sample. The diluted sample will no longer match 0.5 MacFarland standard. Incorrect results will be obtained in Disk diffusion test due to overgowth of bacterial population.

If the dilution made by Trent was used for Disk Diffusion test, it would give rise to incorrect results. As the dilution contained heavy bacterial population, it would give rise to smaller zone of inhibition. The Minimum inhibotory concentration(MIC) obtained will also be incorrect.

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