Abstract
A plasmid (pYM3) carrying a fused gene ada'-'lacZ was introduced into Salmonella typhimurium TA1535 to give a strain designated TA1535/pYM3. Using this strain and the strain TA1535/pSK1002 (umuC'-'lacZ), the activity of β-galactosidase induced by DNA-damaging agents was measured by a fluorometric assay. This strain responded only to alkylating agents such as N-methyl-N′-nitro-N-nitrosoguanidine (MNNG). The sensitivity of fluorometric assay was compared to that of the original colorimetric assay. It was found that the sensitivities were almost equal, but that the amount of substance required in the assay was about thirty times less.
The fluorometric umu- and ada-test was also employed for the detection of mutagens in food, in comparison with the Ames test. Japanese chopped ham was tested for mutagenic activity after nitrite treatment and fractionation. All fractions gave positive results in this sensitive fluorometric assay and in the Ames test.
The fluorometric umu- and ada-test is advantageous for assaying small amounts of various food samples. The ada-test may be useful for the screening of potential DNA-methylating agents in food samples.
