DEVELOPMENT AND ITS PRACTICAL USE OF SCREENING METHODS ON HAZARD IDENTIFICATION USING CATALASE MUTANT GENE AS A PREDICTIVE INDEX

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This research aimed at developing a screening method for hazard identification using catalase mutant E coli strains constructed by encoding the catalase cDNA from catalase mutant mice (Cs^b) and its corresponding wild type (Cs^a) into catalase-deficient K coli UM255. To assess the cytotoxicity of the chemicals, we employed a CAT assay (a zone of inhibition test of bacterial growth and colony-forming efficiency test using catalase mutant E coli strains). Lawsone exposure inhibited the growth of both Cs^a and Cs^b strains in a dose-dependent manner, in which Cs^b was more susceptible than Cs^a, showing the larger zone of growth inhibition surrounding the paper disc. Natural henna leaves did not show toxic effects, whereas two out of four samples of market henna products were shown toxicity effects. Catalase abolished zone of inhibition of henna products, and low concentration of exogenous MnSOD and Cu/ZnSOD eliminated the toxicity. We also exposed dithiothreitol (DTT) to catalase mutant E coli strains. The results show that DTT was also toxic to the catalase mutant K colis in dose dependent manner and significantly different between Cs^a and Cs^b. Catalase, CuZnSOD, and MnSOD also showed protective ability on tester strains. Treatment with waste disposal extracted by methanol and sterilized water showed a negative relation between the exposure dose and survival of these strains. The results support the usefulness of these newly established strains for hazard identification of oxidative chemicals in a risk assessment process.