Its theoretically possible that naturally occurring contamin

It\'s theoretically possible that naturally occurring (contaminating) bacteria that happen to be ampicillin resistant could be yielding the colonies observed. Describe a NEGATIVE CONTROL experiment that could be run in parallel to test for this possibility?

Solution

In this case for making negative control one must take bacteria present in its natural condition where no transfer of ampicillin resistant gene has been done. As and when this condition is maintained where bacteria lacks ampicillin resistant gene, then by applying ampicillin from outside during plating of bacteria the population density seems to decrease. This clearly shows lack of ampicillin resistivity hence NEGATIVE CONTROL experiment gets completed.