Detection of the Toxigenicities for Bacillus cereus and Bacillus thuringiensis and Assay of the Insecticidal Activity for B. thuringiensis
| Autor: | Jen-Chieh Pang, 龐仁傑 |
|---|---|
| Rok vydání: | 2000 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 88 Based on the results of this study, B. thuringiensis strains may possess all the major enterotoxigenic factors found in B. cereus strains. Of the 76 B. thuringiensis (including 64 nature strains) and 84 B. cereus strains studied, the ratio of toxigenic strains found in B. thuringiensis strains was higher than that in B. cereus strains. When the gel diffusion assays were used for the measurement of hemolysin BL activity, it was found that distinct discontinuous hemolytic patterns were observed both on the blood agar made with goat serum (blood agar I) and calf serum (blood agar II). In general, formation of the discontinuous hemolytic patterns on blood agar I was rapid and the pattern was clear in comparison to these on blood agar II. In comparison to the results obtained at 22, 25, 30, 32, 37℃, high temperature allowed the formation discontinuous patterns was rapidly. The optimum condition for gel diffusion assay is that using blood agar I and incubation at 37℃ for 18 ~ 24 hrs. On study of the cytotoxicity to the cultured cells, it was found that all the tested B. cereus and B. thuringiensis strains showed toxicity to Vero, CHO and HEp-2 cells. Of those three cell lines tested, CHO cell is most sensitive to the Bacillus toxigenicity followed by Vero cell and HEp-2 cell. On study of the enterotoxigenicity for HBL toxin using BCET-RPLA kit and the cytotoxicity to the cultured cells, it was found that B. thuringiensis strains generally shown comparable toxigenicity as the B. cereus strains. Thus, screening of B. thuringiensis strains without enterotoxigenicity or with low cytotoxicity for the production of B. thuringiensis insecticidal toxin is important on the food safety view. This is one of the major purposes of this research. Though the above described cytotoxicity assay and the insecticidal activity analysis using diamond-back moth (Plutella xylostella), we found that of the 61 B. thuringiensis strains studied, two strains, termed as T13 and T20, showed low cytotoxicity and high insecticidal activity. On evaluation of the commercial B. thuringiensis insecticide products, it was found that after optimal dilution of those products for insecticide use, they were no cytotoxicity to CHO cell although the spore of those products might cause the food-poisoning cases. In conclusion, we found that it is difficult to isolate B. thuringiensis strains with low enterotoxigenicity but high insecticidal activity. Thus, the possibility for cloning of the cry gene of B. thuringiensis cells into other Bacillus strains, such as B. subtilis strains for the production of B. thuringiensis toxin will be studied by this laboratory in the future. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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