Ames Test

The Ames test, named for its developer, Bruce Ames, is a method to test chemicals for their cancer-causing properties. It is used by cosmetic companies, pharmaceutical manufacturers, and other industries that must prove that their products will not cause cancer in humans.

Ames, a cancer researcher at the University of California, began development of his method in the late 1950s. He believed an efficient, less-expensive means could be found to screen substances than the cumbersome methods in use. He hit upon the use of bacteria, which could be grown (cultured) cheaply, and grew rapidly so that testing could be completed quickly, yet could indicate the carcinogenic (cancer-causing) potential of many chemicals.

The bacterium used is a strain of Salmonella typhimurium that lacks an enzyme needed to form colonies. The bacterium is grown on agar culture (agar is a gelatin-like substance with nutrients). The substance to be tested is blotted on a bit of paper and placed on the agar. If the substance is a carcinogen it will cause mutations in the bacterium as the cells divide. The mutant cells will have the enzyme to form colonies. The test can be completed in a day.

Bacterial mutations are the result of DNA damage. Because DNA in bacteria is similar to that in the higher animals, it is assumed the substance also will damage DNA in those animals and cause cell mutations and possibly cancer.

The Ames test is a screening test; it is not the final test that any substance must undergo before being commercially produced. It is designed to detect a cancer-causing agent quickly and inexpensively.

Prior to development of this test the procedure to determine whether a substance was a carcinogen required feeding the test substance to or injecting it into laboratory animals such as rats or mice and then examining them for evidence of tumor formation. Testing took years to complete, hundreds of animals, and millions of dollars.

Any substance that causes bacterial mutation in the Ames test is not given further consideration for development. A substance that does not produce bacterial mutation still must undergo animal testing, but at least the manufacturer has a good idea that it is not a cancer-causing agent.