Effects of Gamma Irradiation on Wheat Gluten

The effects of γ-irradiation on wheat gluten were studied by means of gel filtration on Sephadex G-100, starch gel electrophoresis and analysis of amino acid composition. Analyses of gluten at a moisture content of 2% revealed no significant change in amino acid composition except for cystine which was decreased by about 8% with irradiation at 10 Mrad. Changes in the chromatogram from gel filtration were interpreted in terms of random depolymerization resulting from irradiation. The results of starch gel electrophoresis suggested that irradiation levels greater than 3 Mrad resulted in characteristic changes in the molecular configuration of gliadin components.     

Characterization of Bacillus pumilus E601 Spores After Single Sublethal Gamma Irradiation Treatments

Eighteen survivor strains of Bacillus pumilus E601 have been isolated after single sublethal irradiation treatments with ⁶⁰Co. Primary isolation was based on the loss of motility and pellicle formation. However, with subsequent subcultivation, eight isolates reverted back to the standard of exhibiting motility and pellicle formation. Characteristics of the isolates include alterations in spore radiation resistance and in the amino acid requirements for spore germination and outgrowth. Other alterations in cultural and physiological characteristics were found. Three of the isolates were asporogenous.     

Effects on Growth and Toxin Production of Exposure of Spores of Clostridium botulinum Type F to Sublethal Doses of Gamma Irradiation

Spores of the Langeland strain of Clostridium botulinum type F were grown at 30 or 10 C after exposure to 0.0, 0.1, or 0.2 megarad of cesium-137 gamma irradiation. When incubated at 30 C, cultures irradiated at the 0.2-megarad level reached the stationary growth phase 15 hr earlier than the 0.0 or 0.1 megarad-irradiated cultures. This was not the result of earlier or more frequent germination of the irradiated spores, the formation of larger individual cells, filament formation, or cell clumping. It appeared to result from elimination of a lytic phenomenon noted in 0.0 and 0.1 megarad-irradiated cultures after 26 and 29 hr of incubation, respectively, which was followed by a second exponential-growth response 5 hr later in these cultures. The time of toxin appearance in culture supernatant fractions was independent of prior irradiation treatment and occurred after 36 hr of incubation. Toxin release was essentially logarithmic until maximal titers were reached and maximal toxin titers were higher in irradiated than in unirradiated cultures. The higher toxin level was sustained over a period of 23 days of 30 C. Toxin produced in the 30 C cultures could not be trypsin-activated. An incubation temperature of 10 C resulted in no outgrowth of spores subjected to 0.2 megarad of irradiation, although spore germination did occur. At 10 C, outgrowth of the 0.1-megarad culture was faster with slightly higher quantities of a more stable toxin than was seen in the unirradiated control. At 10 C, trypsinization was necessary to demonstrate the toxin present in the cultures.     

Chlorine Inactivation of Spores of Encephalitozoon spp.

This report is an extension of a preliminary investigation on the use of chlorine to inactivate spores of Encephalitozoon intestinalis and to investigate the effect of chlorine on two other species, E cuniculi and E. hellem, associated with human infection. The 50% tissue culture infective doses of these three species were also determined. On the basis of the results obtained, it appears that chlorination of water is an effective means of controlling spores of these organisms in the aquatic environment.     

Role of Disulphide Bonds in the Resistance of Bacillus cereus Spores to Gamma Irradiation and Heat

S ummary . Spores of Bacillus cereus were treated with thioglycollic acid which ruptures at least 10–30% of the spore disulphide bonds by reducing them to thiol groups. The treated spores were still viable and were sensitive to lysozyme but remained as resistant to γ-irradiation and to heat as untreated spores. Neither treated nor untreated spores were sensitized to irradiation by reagents which block thiol groups. The results did not indicate that the high content of disulphide bonds in spore coat protein protects spores against inactivation by irradiation or heat.     

Inactivation of Dried Bacteria and Bacterial Spores by Means of Gamma Irradiation at High Temperatures

Dried preparations with Streptococcus faecium, strain A(2)1, and spores of Bacillus sphaericus, strain C(I)A, normally used for control of the microbiological efficiency of radiation sterilization plants and preparations with spores of Bacillus subtilis, normally used for control of sterilization by dry heat, formalin, and ethylene oxide, as well as similar preparations with Micrococcus radiodurans, strain R(1), and spores of Bacillus globigii (B. subtilis, var. niger) were gamma irradiated with dose rates from 16 to 70 krad/h at temperatures from 60 to 100 C. At 80 C the radiation response of the spore preparations was the same as at room temperature, whereas the radiation resistance of the preparations with the two vegetative strains was reduced. At 100 C the radiation response of preparations with spores of B. subtilis was unaffected by the high temperature, whereas at 16 and and 25 krad/h the radiation resistance of the radiation-resistant sporeformer B. sphaericus, strain C(I)A, was reduced to the level of radiation resistance of preparations with spores of B. subtilis. It is concluded that combinations of heat and gamma irradiation at the temperatures and dose rates tested may have very few practical applications in sterilization of medical equipment.     

Efficacy of the Inactivation of Bacterial Spores in White Petrolatum and a Hydrophilic Ointment by Gamma Irradiation

To evaluate the possibilities of using gamma irradiation for the sterilization of ointments, the effect of irradiation on spores of Bacillus pumilus and Bacillus sphaericus in dry material and in two different kinds of ointments was studied. The results indicate that for sterilization purposes irradiation was less effective in white petrolatum as compared to irradiation in the dry state. No such protective effect was found in a hydrophilic ointment. Accordingly, the sterilization dose needed for the sterilization of an ointment can be decided upon only after inactivation experiments with suitable test organisms in the actual preparation.     

Survival of Clostridium botulinum Spores

Radiation survival curves of spores of Clostridium botulinum strain 33A exhibited an exponential reduction which accounted for most of the population, followed by a “tail” comprising a very small residual number [7 to 0.7 spore(s) per ml] which resisted death in the range between 3.0 and 9.0 Mrad dose levels. The “tail” was not caused by protective spore substances released into the suspensions during irradiation, by the presence of accumulated radiation “inactivated” spores, or by heat shock of pre-irradiated spores. The theoretical number of spore targets which must be inactivated by irradiation was estimated both by a graphical and by a computation method to be about 80, and the D value was calculated to be 0.295 and 0.396 Mrad, respectively, in buffer and in pork pea broth.     

Effects of Irradiation on the Survival of Virus in West Coast Oysters

Gamma irradiation was evaluated as a means of inactivating poliovirus in shucked and whole shellfish. Results indicated that there was a significant survival of virus at all levels of radiation tested.     

Gamma Irradiation of Stentor polymorphus

SYNOPSIS. Stentor polymorphus was irradiated with ⁶⁰Co gamma rays at 525 rads/minute to examine the effect on survival, cell division, oral membranellar frequency and oxygen uptake. Both survival and cell division were studied on single cells. The LD₅₀ is 285 kilorads but cell division is inhibited below this dose; 110 kilorads doubles the 1st post-irradiation division interval, and a delay of 240 hours occurs at the maximum tolerated dose of 310 kilorads. Conjugating cells are more sensitive, with an LD₅₀ of approximately 40 kilorads.
The frequency of cilia in the membranellar band, measured stroboscopically, is reduced by 30% after 14.5 kilorads, and stopped by higher doses. Recovery has a similar time scale to recovery of fission. A Clarke electrode was used to measure changes in oxygen uptake after irradiation. Depressions of up to 50% were found. Recovery followed a similar pattern to that of ciliary activity and cell division.     

Effect of Gamma Irradiation on the Amino Acid of Potatoes

The free amino acids of potatoes irradiated with the doses of 7,000, 15,000 and 30,000 rad were determined by ion-exchange chromatography.

After 15 days storage following irradiation, it was shown that the concentration of asparatic acid, proline and aliphatic amino acids increased with increasing irradiation doses, while that of basic amino acids and glutamic acid especially decreased. However, after 105 days of storage, the similarity of the free amino acid content of irradiated potatoes to that of non-irradiated and non-stored potatoes was observed.

On the concentration of protein-bound amino acids, there were no significant differences between non-irradiated and 15,000 rad irradiated potatoes.     

Survival of Bacillus thuringiensis Spores in Soil

Bacillus thuringiensis spores and parasporal crystals were incubated in natural soil, both in the laboratory and in nature. During the first 2 weeks, the spore count decreased by approximately 1 log. Thereafter, the number of spore CFU remained constant for at least 8 months. B. thuringiensis did not lose its ability to make the parasporal crystals during its residence in soil. Spore survival was similar for a commercial spore-crystal preparation (the insecticide) and for laboratory-grown spores. In contrast to these results, spores that were produced in situ in soil through multiplication of added vegetative cells survived for only a short time. For spore additions to soil, variations in soil pH had little effect on survival for those spores that survived the first 2 weeks of incubation. Also without effect were various pretreatments of the spores before incubation in soil or nutritional amendment or desiccation of the soil. Remoistening of a desiccated soil, however, caused a decrease in spore numbers. Spores incubated in soil in the field did not show this, but the degree of soil desiccation in nature probably never reached that for the laboratory samples. The good survival of B. thuringiensis spores after the first 2 weeks in soil seemed to be a result of their inability to germinate in soil. We found no evidence for the hypothesis that rapid germination ability for spores in soil conferred a survival advantage.     

Comparison of UV Inactivation of Spores of Three Encephalitozoon Species with That of Spores of Two DNA Repair-Deficient Bacillus subtilis Biodosimetry Strains

When exposed to 254-nm UV, spores of Encephalitozoon intestinalis, Encephalitozoon cuniculi, and Encephalitozoon hellem exhibited 3.2-log reductions in viability at UV fluences of 60, 140, and 190 J/m², respectively, and demonstrated UV inactivation kinetics similar to those observed for endospores of DNA repair-defective mutant Bacillus subtilis strains used as biodosimetry surrogates. The results indicate that spores of Encephalitozoon spp. are readily inactivated at low UV fluences and that spores of UV-sensitive B. subtilis strains can be useful surrogates in evaluating UV reactor performance.     

The Combined Effect of Hydrogen Peroxide and Ultraviolet Irradiation on Bacterial Spores

Ultra-violet (u.v.) light irradiation of spores of Bacillus subtilis in the presence of hydrogen peroxide produced a rapid kill which was up to 2000-fold greater than that produced by irradiation alone. A kill of 99–99% was produced by 30s u.v. irradiation of spores of 6 strains of Bacillus and Clostridium in the presence of hydrogen peroxide 1.0 g/100 ml but with the more resistant spores of 9 further strains, irradiation in the presence of hydrogen peroxide 2–5 g/100 ml followed by mild heating was required.