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Chemicals mutagenic in Salmonella typhimurium strain TA1535 but not in TA100

M J Prival1, E Zeiger

  • 1Genetic Toxicology Branch (HFS-236), Food and Drug Administration, Washington, DC 20204, USA. mprival@bangate.fda.gov

Mutation Research
|May 26, 1998
PubMed

Insights

The Salmonella typhimurium assay uses strains TA1535 and TA100 to detect mutagens. Strain TA1535 uniquely identifies 5% of mutagens, warranting further investigation into its inclusion in routine testing.

Area of Science:

  • Toxicology
  • Genetics
  • Microbiology

Background:

  • The Salmonella mutagenicity assay is a standard tool for detecting chemical mutagens.
  • Two key strains, Salmonella typhimurium TA1535 and TA100, share a base pair substitution mutation but differ in the presence of the pKM101 plasmid, which enhances SOS mutagenesis in TA100.
  • Strain TA100 is generally more sensitive, prompting questions about the necessity of including strain TA1535 in routine testing batteries.

Purpose of the Study:

  • To evaluate the contribution of Salmonella typhimurium strain TA1535 to mutagenicity testing.
  • To determine the proportion of mutagens detected by TA1535 that are missed by TA100.
  • To inform decisions regarding the inclusion of strain TA1535 in the core battery of Salmonella assay strains.

Main Methods:

  • Analysis of data from the National Toxicology Program's screening protocol involving 659 chemicals tested in the Salmonella assay.
  • Comparison of results between Salmonella typhimurium strains TA1535 and TA100.
  • Identification of chemicals positive in TA1535 but negative or equivocal in TA100.

Main Results:

  • Out of 659 chemicals identified as mutagens, 36 (5%) were positive in strain TA1535 but not in strain TA100.
  • Of these 36 chemicals, 23 were negative and 13 were equivocal in strain TA100.
  • For three specific chemicals (acetaldehyde oxime, 6-mercaptopurine, and 1,3-butadiene), the increase in revertants in TA1535 significantly exceeded that in TA100.

Conclusions:

  • Strain TA1535 uniquely identifies a small but significant percentage of mutagens missed by strain TA100.
  • The higher spontaneous background in TA100 may obscure low-level positive results detected in TA1535.
  • Further research on the reproducibility, mechanisms, and relevance of unique TA1535 positives is needed to decide its role in routine Salmonella mutagenicity testing.

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