Ames test

Ames test
Histidine · CC BY-SA 3.0 · source
Name	Ames test
Purpose	Detect mutagenic potential of chemical compounds
Developed	1970s
Inventor	Bruce Ames
Method	Bacterial reverse mutation assay
Organisms	Salmonella typhimurium, Escherichia coli

Ames test

The Ames test is a biological assay that uses specially engineered strains of Salmonella enterica (historically referred to as Salmonella typhimurium) and sometimes Escherichia coli to assess the mutagenic potential of chemical compounds. Developed in the 1970s by Bruce Ames, it links mutagenicity to potential carcinogenesis and has influenced regulatory frameworks such as those from the U.S. Food and Drug Administration, Environmental Protection Agency, and International Agency for Research on Cancer. The assay integrates microbiology, toxicology, and metabolic activation concepts derived from research at institutions like the University of California, Berkeley and the National Institutes of Health.

Introduction

The assay was devised to provide a rapid, inexpensive screen for point-mutagenic activity using auxotrophic bacterial strains derived from classical genetics studies pioneered by researchers at institutions including Cold Spring Harbor Laboratory and Carnegie Institution for Science. Its adoption followed interest from agencies such as the National Toxicology Program and scholarly discussion in venues including the Proceedings of the National Academy of Sciences and the Journal of Bacteriology. Early users included laboratories at the Oak Ridge National Laboratory and pharmaceutical companies such as Pfizer and GlaxoSmithKline.

Principle and methodology

The core principle is detecting reverse mutations that restore prototrophy in histidine-dependent or tryptophan-dependent bacterial strains. Test compounds are plated with auxotrophic bacteria on minimal media in experiments analogous to classical assays by researchers at Cambridge University and the Max Planck Society. Many protocols couple bacterial exposure to an exogenous metabolic activation system (S9 mix) derived from rodent liver microsomes prepared from animals treated at facilities like the National Institute of Environmental Health Sciences and earlier metabolic studies at The Rockefeller University. Standard methods are described by panels convened by Organisation for Economic Co-operation and Development and validation efforts coordinated with the International Organization for Standardization.

Test strains and controls

Common strains include several auxotrophic derivatives developed from foundational bacterial genetics and mutagenesis studies at institutions tied to scientists such as Seymour Benzer and Joshua Lederberg. These strains contain specific mutations in genes involved in amino acid biosynthesis and additional modifications that increase sensitivity to mutagens, such as defects in cell wall permeability and DNA repair pathways characterized in work at Massachusetts Institute of Technology and Stanford University. Positive controls typically use known mutagens studied by laboratories like those at Harvard University and the Karolinska Institutet, while negative controls rely on solvent and vehicle controls standardized by bodies such as the World Health Organization and regulatory authorities including the European Medicines Agency.

Variants and adaptations

Numerous variants adapt the original assay for different needs: modifications for testing volatile compounds were developed in collaboration with industrial researchers at BASF and Dow Chemical Company; high-throughput adaptations emerged from research groups at Lawrence Berkeley National Laboratory and biotechnology firms such as Amgen; and combined bacterial-yeast systems draw on genetics work from the University of Cambridge and the University of Tokyo. Some laboratories integrate complementary mammalian cell assays promoted by organizations like the Organisation for Economic Co-operation and Development to satisfy requirements from regulators including the European Chemicals Agency and the U.S. Environmental Protection Agency.

Interpretation and limitations

A positive result indicates an increased frequency of reverse mutations under the test conditions and has been correlated with carcinogenicity in rodent bioassays run by the National Toxicology Program and long-term studies at institutions such as the National Cancer Institute. However, the assay can yield false positives and false negatives; these limitations were explored in comparative programs involving the International Agency for Research on Cancer and consortium studies including academic groups at the University of California, San Francisco. Metabolic activation by S9 does not fully recapitulate human biotransformation pathways characterized by research on human cytochrome P450 enzymes at centers like the University of Washington and Johns Hopkins University, so follow-up testing with mammalian systems or transgenic models (developed by teams at the Jackson Laboratory and Lawrence Livermore National Laboratory) is often required. Statistical interpretation follows standards from bodies such as the International Conference on Harmonisation of Technical Requirements for Registration of Pharmaceuticals for Human Use.

Applications and regulatory significance

The assay is widely used in preliminary screening by chemical manufacturers like Shell and pharmaceutical companies such as Novartis and Roche; it informs regulatory decision-making by agencies including the U.S. Food and Drug Administration, European Medicines Agency, and Environmental Protection Agency. It contributed to hazard classifications coordinated by the Globally Harmonized System of Classification and Labeling of Chemicals and testing strategies in programs run by the Organisation for Economic Co-operation and Development. In environmental monitoring, data from Ames assays have been applied in assessments by the United Nations Environment Programme and remediation efforts overseen by agencies like the U.S. Department of Energy.

Category:Assays Category:Toxicology Category:Genetics