A mutagenic effect (increase in revertant colony numbers as compared to control counts) was not observed for any of the valerian extracts tested up to the concentration of 5000 [micro]g/plate in any of the 5 test strains in two independent experiments with and without metabolic activation (plate incorporation and pre-incubation test, respectively), even if common regulatory thresholds of 2 (for strains TA 98, TA 100, TA 1535 and TA 1537) or 1.
Significantly increasec values compared to NR point to a potential enhancement of revertant rates, reduced values to cytotoxicity.
Juices from ten citrus varieties reduced significantly the number of revertant
colonies induced by N-nitro-o-phenylenediamine (NPD) in TA 97a and sodium azide in TA 100 strains of Salmonella typhimurium (Bala & Grover, 1989).
Significant increases in the number of revertant
colonies were induced by the known mutagens and carcinogens sodium azide, 2-nitrofluorene, 2-aminoanthracene when tested under the same conditions (Meester and Leonard, 1988).
2]) indicated a count of more than twice the revertant
colonies of TA 102 as the negative control.
Pseudogene rp028 was inactivated in a virulent E strain but not in its virulent revertant Evir strain (9).
E strain and its revertant Evir strain differed by a single nucleotide insertion in E strain at position 732 in rp028, which we reported previously (9).
Concentrations needed for 50% inhibition of mutagen-induced revertant formation was found to be 5 mg/plate.
The plates were incubated for 48 h at 37[degrees]C and the revertant colonies were counted using a colony counter.
25-100 [micro]g/plate was also checked for possible toxic or mutagenic effects in both TA98 and TA100 strains and no change in spontaneous revertant
count indicated absence of any mutagenic/toxic effects of DBM in the tested dose range (see footnote of Tables 1-3 for revertant
colonies were scored after 48 hrs of incubation.
colonies were counted, and the toxic effect was determined by viewing the background lawn under a stereo microscope.