Recommendations for the performance of bacterial mutation assays

Introduction:
This text is a summary of the recommendations from an international workshop on the standardization of genotoxicity test procedures, specifically focusing on bacterial mutation assays. The recommendations cover various aspects of the study design, including the bacterial test strain battery, test system, dose-setting, study design, controls, criteria for a positive result, and the need for test repetition. The recommendations aim to create a minimum standard experimental design based on valid supportive data.

Key Points:

* Bacterial mutation assays, such as the Salmonella/microsome assay or ames test, have become widely used for mutagenicity screening.
* The working group recognized that certain classes of mutagen may not be detected using standard procedures, and recommended alternative procedures for their detection.
* The group agreed on the use of specific bacterial strains and metabolic activation systems, and provided recommendations on test concentrations and study design.
* There was no consensus on the use of specific positive control compounds, but it was recommended that individual laboratories select positive control chemicals based on their own database.
* The group agreed that for non-toxic freely soluble test agents, an upper limit of 5 mg/plate should be tested, while for insoluble or toxic compounds, the recommendations were the same as those for other in vitro tests.
* a consensus was reached on the need to carry out further tests if equivocal results are obtained in the initial test, although the design of the repeat study should be left flexible.
* The group recognized that certain classes of mutagen may not be appropriately tested using bacterial mutation assays, such as highly bactericidal compounds or those that interfere specifically with mammalian cell replication systems.

Main Message:
The recommendations provided in this summary aim to create a standardized and harmonized protocol for bacterial mutation assays. While certain aspects, such as the composition of the optimum bacterial test battery and the need to further evaluate negative results using an alternative methodology, did not reach consensus, the majority of the recommendations reflect the scientific consensus on best practices for conducting these assays. The summary acknowledges the limitations of bacterial mutation assays and highlights the importance of considering alternative procedures for specific classes of mutagens. Overall, the recommendations emphasize the need for careful study design, appropriate controls, and the use of valid scientific judgment in interpreting the results of these assays.

Gatehouse, D., S. haworth, T. Cebula, E. Gocke, L. Kier, T. Matsushima, C. Melcion, et al. “Recommendations for the Performance of Bacterial Mutation assays.” Mutation Research/Environmental Mutagenesis and Related Subjects 312, no. 3 (June 1994): 217–33. https://doi.org/10.1016/0165-1161(94)90037-X.