In the newly-constructed Salmonella strains SB1111 (hisC3018) and SB1106 (hisC3108, his01242), the mutagenic effects of H202 were observed at doses similar to those used with other strains. This C3108 mutation is reverted by H202 in the absence of the uvrB deletion, pKM101 plasmid, or the rfa mutation, which appear necessary for mutagenesis in strains TA97, TA102, and TA104. Incorporation of the pKM101 plasmid enhanced the reversion of SB1111 and SB1106 (SB1111p and SB1106p). SB1106p is comparable to TA104 in its spontaneous reversion rate, but is more sensitive to H202 mutagenesis. The spontaneous rate of SB1111p, on the other hand, was too high for routine use. Strain SB1106p is being used to test other chemicals, such as thiols, that may act through the formation or release of H202, to determine its utility for routine chemical testing. The use of electrochemical detection coupled with HPLC procedures allow the effective monitoring of DNA for the induction of oxygen-damaged products, such as 8-hydroxyguanosine (8-OH-dG). This technique has been used to monitor the induction of 8-OH-dG in purified DNA by H202 or glutathione. In the presence of a Fenton reaction mix, glutathione induced a doubling of the background rate of 8-OH-dG in purified deoxyguanosine. 8-OH-dG was also detected in DNA samples subjected to various enzymatic digestion techniques. The levels of 8-OH-dG in DNA from calf thymus, rat liver, or Salmonella is high enough to mask low levels of induction by chemicals. New methods for DNA extraction and digestion are being adopted in an attempt to lower the background levels of 8-OH-dG.
