You perform a Kirby-Bauer assay, but you neglect to use aseptic technique. Your

Question

You perform a Kirby-Bauer assay, but you neglect to use aseptic technique. Your plate becomes contaminated with a bright red organism. You can easily tell this organism apart from the one you intended to inoculate (which has grown into a nice lawn all over the plate). In order to conserve time, you measure the zone of inhibition for your intended organism, ignoring the contaminants. Are you assured to get the correct answer using this method?

A. Yes, but you have to factor in the zone of inhibition for the contaminant as well. B. No, the contaminant adds too many variables to make this assay usable. C. Yes, but you would have to subtract 1–2 mm from the intended organism’s zone of inhibition to account for the presence of the contaminant. D. Yes, you can easily tell the two organisms apart, ensuring that you measure only the zone of inhibition for the correct organism.

Explanation / Answer

No, because the contamination adds to many variables to make this assay usable.

Hence, the correct option is (B).

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