The Ames test is a biological assay to assess the mutagenic potential of chemical compounds. As cancer is often linked to DNA damage, the test also serves as a quick assay to estimate the carcinogenic potential of a compound since the standard tests for carcinogenicity done on rodents take years to complete and are expensive to do. The procedure is described in a series of papers from the early 1970s by Bruce Ames and his group at the University of California, Berkeley. Also known as a biological assay, a bioassay is a measurement of the effects of a substance on living organisms. ... In biology, a mutagen (Latin, literally origin of change) is an agent that changes the genetic information (usually DNA) of an organism and thus increases the number of mutations above the natural background level. ... Cancer is a class of diseases or disorders characterized by uncontrolled division of cells and the ability of these to spread, either by direct growth into adjacent tissue through invasion, or by implantation into distant sites by metastasis (where cancer cells are transported through the bloodstream or lymphatic system). ... The structure of part of a DNA double helix Deoxyribonucleic acid, or DNA, is a nucleic acid molecule that contains the genetic instructions used in the development and functioning of all known living organisms. ... In pathology, a carcinogen is any substance or agent that promotes cancer. ... Suborders Sciuromorpha Castorimorpha Myomorpha Anomaluromorpha Hystricomorpha Rodentia is an order of mammals also known as rodents. ... Bruce Ames, by ItalianScallion Bruce Ames (born December 16, 1928), is a professor of Biochemistry and Molecular Biology at the University of California, Berkeley, and a senior scientist at Childrens Hospital Oakland Research Institute (CHORI). ... Sather tower (the Campanile) looking out over the San Francisco Bay and Mount Tamalpais. ...

General procedure

The test uses several strains of the bacterium Salmonella typhimurium that carry mutations in genes involved in histidine synthesis, so that they require histidine for growth. The variable being tested is the mutagen's ability to cause a reversion to growth on a histidine-free medium. The tester strains are specially constructed to have both frameshift and point mutations in the genes required to synthesize histidine, which allows for the detection of mutagens acting via different mechanisms. Some compounds are quite specific, causing reversions in just one or two strains. ^[1] The tester strains also carry mutations in the genes responsible for lipopolysaccharide synthesis, making the cell wall of the bacteria more permeable, ^[2] and in the excision repair system to make the test more sensitive. ^[3] Rat liver extract is added to simulate the effect of metabolism, as some compounds, like benzopyrene, are not mutagenic themselves but their metabolic products are.^[4] Binomial name Salmonella enterica Salmonella enterica is a species of Salmonella bacterium. ... Histidine is one of the 20 most common natural amino acids present in proteins. ... Framing error is the following: Generally, a framing error is the result of reading a string of symbols which are grouped in blocks starting at the wrong point. ... A point mutation, or substitution, is a type of mutation that causes the replacement of a single base nucleotide with another nucleotide. ... It has been suggested that mutant be merged into this article or section. ... Lipopolysaccharide (captions are in French) Lipopolysaccharide (LPS) is a large molecule consisting of a lipid and a polysaccharide (carbohydrate) joined by a covalent bond. ... A cell wall is a fairly rigid layer surrounding a cell, located external to the cell membrane, that provides the cell with structural support, protection, and a filtering mechanism. ... A few of the metabolic pathways in a cell. ... Benzo[a]pyrene, C20H12, is a five-ring polycyclic aromatic hydrocarbon that is mutagenic and highly carcinogenic. ...

The bacteria are spread on an agar plate with a small amount of histidine. This small amount of histidine in the growth medium allows the bacteria to grow for an initial time and have the opportunity to mutate. When the histidine is depleted only bacteria that have mutated to gain the ability to produce its own histidine will survive. The plate is incubated for 48 hours. The mutagenicity of a substance is proportional to the number of colonies observed. This does not adequately cite its references or sources. ...

Problems

As Salmonella is a prokaryote, it is not a perfect model for humans. An adapted in vitro model has been made for eukarotic cells, for example yeast cells.

References

1. ^ Bruce N. Ames, E. G. Gurney, James A. Miller, and H. Bartsch (1973). "Carcinogens as Frameshift Mutagens: Metabolites and Derivatives of 2-acetylaminofluorene and other Aromatic Amine Carcinogens". PNAS 69: 3128-2132.  PDF
2. ^ Bruce N. Ames, Frank D. Lee, and William E. Durston (1973). "An Improved Bacterial Test System for the Detection and Classification of Mutagens and Carcinogens". PNAS 70: 782-6.  PDF
3. ^ Joyce McCann, Neil E. Spingarn, Joan Kobori, and Bruce N. Ames (1975). "Detection of Carcinogens as Mutagens: Bacterial Tester Strains with R Factor Plasmids". PNAS 72: 979-83.  PDF
4. ^ Bruce N. Ames, William E. Durston, Edith Yamasaki, and Frank D. Lee (1973). "Carcinogens are Mutagens: A Simple Test System Combining Liver Homogenates for Activation and Bacteria for Detection". PNAS 70: 2281-5.  PDF