Effects of gamma radiation on Clostridium botulinum type E under various parameters

Spores of Clostridium botulinum type E strain Eklund (Eklund) was irradiated with gamma radiation and its recovery was tested on the tryptone-peptone-glucose-yeast extract-agar (TPGYA) containing various levels of NaCl and Na-thioglycollate. The presence of 0.5% or more NaCl in the media decreased the viable counts, while Na-thioglycollate of up to 0.15% did not affect the recovery of both irradiated and non-irradiated spores. Eklund spores were also irradiated under air (21% O2), N2O and N2, with or without the additive of one of the following agents (additive/concentration): disodium ethylenediaminetetraacetate (EDTA), 0.01 M; t-butanol, 0.1 M; NaCl, 0.01 M; catalyze, 10 mg/ml and DL-cysteine, 0.1 mM. Radiation process was most effective in destroying the spores when carried out under air (21% O2), followed by N2O and N2. Among the additives tested, EDTA was the most efficient protector followed by t-butanol when irradiation process was carried under N2O and N2 gas environment. Catalase and DL-cysteine sensitized the spores when irradiated under N2O and N2, while NaCl only sensitized under N2. Spores kept frozen at -750C for 30 days but thawed prior to irradiation were more sensitive to radiation damage than freshly prepared spores. Radiation resistance of the spores increased when 15% glycerol was added to the phosphate bugger (0.06 M, pH 7.0) and used as suspending media. When the concentration of the spore increased from 106/ml to 1011/ml, the radiosensitivities also increased. Seven strains of C. botulinum type E were screened for plasmids by agarose gel electrophoresis