Improvement of the Ames Test Using Human Liver S9 Preparation

The use of the human S9 fraction in mutagenicity testing systems may be valuable for evaluating the mutagenicity of chemicals in humans. When using a crude human liver S9 fraction, which is obtained following the centrifugation of the tissue homogenate for 20 min at 9000g , in the Ames test, we may sometimes find contaminating bacterial colonies and/or an increasing number of His⁺ revertant colonies of tester strains over the normal range on plates in a solvent control. To solve this problem, it is useful to use a purified fat- and bacteria-free human liver S9 fraction of high quality. Such a purified S9 fraction can be obtained by a simple modification to the crude S9 preparation: complete removal of fat after the centrifugation of the crude S9 fraction. This chapter states the experimental protocol for an improved Ames test using a modified human liver S9 preparation, especially highlighting our simple S9 preparation procedure for the Ames test.