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An evaluation of tests using DNA repair-deficient bacteria for predicting genotoxicity and carcinogenicity. A report
Abstract:
The detection of DNA-damaging agents by repair-deficient bacterial assays is based on the differential inhibition of growth of repair-proficient and repair-deficient bacterial pairs. The various methodologies used are described and recommendations are made for their improved use. In a survey of the literature through April 1979, 91 of 276 papers evaluated contained usable data, resulting in an analysis of 611 compounds that had been assayed in 1 or more of 55 pairs of repair-proficient and repair-deficient strains. The results indicate that (1) a liquid suspension assay is more sensitive than a spot (diffusion) test. In a review of the Escherichia coli polA assay, 45 compounds that gave "No Test" in the spot test were clearly positive or negative in the liquid suspension assay. (2) Of the 21 compounds analyzed by the E. coli polA assay and by other E. coli repair-deficient strains (e.g., rec, uvr, hcr, and exr derivatives of WP2 and AB1157), 10 were in complete agreement in all strains except uvrA strains. This indicates that strains other than polA+/polA- are useful for detecting DNA-damaging agents. However, in selecting strains for use in these assays, care should be taken to consider repair pathway specificity for particular compounds. (3) There was a 78% correspondence between results obtained with E. coli polA and Bacillus subtilis (H17/M45, 17A/45T) rec assay and between E. coli polA and Proteus mirabilis. (4) In a comparison of test results with carcinogenicity data, 44 of 71 (62%) carcinogenic compounds assayed by the polA system were positive, 10 (14%) were negative, and 17 (24%) gave No Test or doubtful results. 7 carcinogens were assayed by other E. coli strains and all were positive. 56 carcinogens were assayed in B. subtilis: 24 (43%) were positive, 9 (16%) were negative, and 23 (41%) gave No Test or doubtful results. Of the 7 carcinogens assayed in P. mirabilis, 6 (86%) were positive and 1 (14%) was negative. (5) The results were analyzed with respect to chemical classes. E. coli polA detected the highest percentage of hydroxylamines and alkyl epoxides. The B. subtilis rec assay detected the highest percentage of nitrosamines and sulfur and nitrogen oxides. It is concluded that some of these test systems are effective tools for the detection of DNA-damaging and potentially carcinogenic compounds, especially if the assay is done in liquid suspension and if more than 1 pair of tester strains is used. Advantages and disadvantages of the assay are discussed and suggestions are made for improvements in the system.
Insights
Repair-deficient bacterial assays effectively detect DNA-damaging agents. Liquid suspension tests are more sensitive than spot tests, and using multiple bacterial strains improves detection accuracy for potentially carcinogenic compounds.
Area of Science:
- Microbiology
- Genotoxicology
- Biochemical Assays
Background:
- Bacterial assays using repair-deficient strains detect DNA-damaging agents by observing differential growth inhibition.
- Various methodologies exist, necessitating recommendations for improved application and interpretation of results.
Purpose of the Study:
- To evaluate the efficacy of repair-deficient bacterial assays in detecting DNA-damaging agents.
- To compare different assay methodologies, bacterial strains, and their correlation with carcinogenicity data.
- To provide recommendations for optimizing these assays for improved sensitivity and accuracy.
Main Methods:
- Literature survey of 276 papers (up to April 1979) identifying 91 with usable data on 611 compounds tested.
- Analysis of 55 pairs of repair-proficient and repair-deficient bacterial strains, including Escherichia coli (polA, rec, uvr, hcr, exr) and Bacillus subtilis (rec assay).
- Comparison of liquid suspension assays versus spot diffusion tests, and correlation of assay results with known carcinogenicity data for various chemical classes.
Main Results:
- Liquid suspension assays demonstrated higher sensitivity than spot tests, correctly classifying 45 compounds missed by the spot test.
- Multiple E. coli strains (polA, rec, uvr, hcr, exr) showed high agreement (90%) in detecting DNA-damaging agents, except for uvrA strains.
- High correspondence (78%) was observed between E. coli polA and Bacillus subtilis rec assays, and E. coli polA and Proteus mirabilis.
- Correlation with carcinogenicity data showed 62% positive results for carcinogenic compounds using the E. coli polA system.
- E. coli polA assay excelled in detecting hydroxylamines and alkyl epoxides, while B. subtilis rec assay was superior for nitrosamines and oxides.
Conclusions:
- Repair-deficient bacterial assays are effective tools for detecting DNA-damaging and potentially carcinogenic compounds.
- Liquid suspension assays and the use of multiple tester strain pairs enhance detection capabilities.
- Careful selection of bacterial strains, considering repair pathway specificity, is crucial for assay reliability.