Why would it be important for the kirby-bauer disc diffusion test to use a standard concentration (number of cells in the sample) of each of the bacterial strains being tested?

It is important to use a standard concentration of each of the bacterial strains in the Kirby-Bauer disc diffusion test because lower or higher concentrations can influence the size of the zone of inhibition. For example, in case if the concentration is high, then a visible amount of growth can take place prior to the antibiotic been able to diffuse very far from the disc.

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