Final answer:
In the Ames test, to identify potential carcinogens, a compound should be treated by incubating it in mammalian liver extract before being tested on bacteria.
Step-by-step explanation:
To identify potential carcinogens using the Ames test, a compound should be treated before being tested on bacteria by incubating it in mammalian liver extract. This step incorporates the activation of procarcinogens by liver enzymes into mutagens that can then interact with the DNA of the test bacteria, often a histidine auxotroph strain of Salmonella typhimurium. The liver extract functions as a simulation of the metabolic process that would occur in a mammalian body, reflecting a more accurate assessment of the compound's mutagenic and potentially carcinogenic properties. After treatment with the liver extract and exposure to the bacteria, the mixture is plated on a medium that lacks histidine. The mutation rate is measured by counting the colonies of bacteria that revert to being able to synthesize histidine, which would indicate a mutagenic effect of the compound tested.