If the media is too thin, what happens in AST?

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Multiple Choice

If the media is too thin, what happens in AST?

In antibiotic susceptibility testing, diffusion of the drug through the agar is what creates the zone of inhibition you read. If the agar is too thin, the antibiotic can spread more quickly and over a larger area, so inhibitory concentrations are established over a wider region than under proper conditions. This makes the zones appear larger, which can mislead you to interpret the organism as susceptible when it might not be under standard conditions. So the main idea is that insufficient thickness allows faster diffusion, producing a false susceptible result. The other scenarios described (drug not penetrating the organism, contamination, or poor growth of the organism) are not caused by the thickness of the medium in this diffusion-based test.

In antibiotic susceptibility testing, diffusion of the drug through the agar is what creates the zone of inhibition you read. If the agar is too thin, the antibiotic can spread more quickly and over a larger area, so inhibitory concentrations are established over a wider region than under proper conditions. This makes the zones appear larger, which can mislead you to interpret the organism as susceptible when it might not be under standard conditions. So the main idea is that insufficient thickness allows faster diffusion, producing a false susceptible result. The other scenarios described (drug not penetrating the organism, contamination, or poor growth of the organism) are not caused by the thickness of the medium in this diffusion-based test.

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