Elimination of Escherichia coli O157:H7 in meats by gamma irradiation.

Undercooked and raw meat has been linked to outbreaks of hemorrhagic diarrhea due to the presence of Escherichia coli O157:H7; therefore, treatment with ionizing radiation was investigated as a potential method for the elimination of this organism. Response-surface methods were used to study the effects of irradiation dose (0 to 2.0 kGy), temperature (-20 to +20 degrees C), and atmosphere (air and vacuum) on E. coli O157:H7 in mechanically deboned chicken meat. Differences in irradiation dose and temperature significantly affected the results. Ninety percent of the viable E. coli in chicken meat was eliminated by doses of 0.27 kGy at +5 degrees C and 0.42 kGy at -5 degrees C. Small, but significant, differences in radiation resistance by E. coli were found when finely ground lean beef rather than chicken was the substrate. Unlike nonirradiated samples, no measurable verotoxin was found in finely ground lean beef which had been inoculated with 10(4.8) CFU of E. coli O157:H7 per g, irradiated at a minimum dose of 1.5 kGy, and temperature abused at 35 degrees C for 20 h. Irradiation is an effective method to control this food-borne pathogen.     

Dynamic light scattering studies of irradiated kappa carrageenan

Investigation of the dynamic behavior of irradiated kappa carrageenan (in KCl) as a function of irradiation dose and temperature was done by dynamic light scattering (DLS). The intensity correlation function (ICF) shifted towards shorter relaxation times with increasing radiation dose as a result of radiolysis. The characteristic decay time distribution function, G(gamma), indicates the presence of fast and slow mode peaks respectively at around 0.1-10 ms and 100-1000 ms. A peak broadening of the fast mode peak in G(gamma) appeared with decreasing temperature, indicating that coil-to-helical conformational transition took place. The conformation transition temperature (CTT) decreased with increasing radiation dose. No transition was observed for kappa-carrageenan irradiated at 200 kGy. A new faster relaxation mode appeared at around 0.1-1 ms at temperatures below the CTT. This peak is found in kappa-carrageenan irradiated at doses exclusively between 75 and 175 kGy. The peak height of this mode is largest at 100 kGy which corresponds to the optimum biologic activity of kappa-carrageenan reported previously.     

The influence of the irradiation regime upon mycotoxins production under experimental conditions

The paper handles the problem of the inactivation of the toxinogenic strain Aspergillus flavus following the application of gamma radiation to wheat. The amount of the applied dose and of the absorbed dose of ionizing radiation upon the inhibition of mycelium growth and toxin production were defined. The aflatoxin B1 was determined by extracting in chloroform and developed on Silufol R within the choroform; aceton system. The applied doses of gamma radiation (3-30 kGy) have show that the absorbed dose does not inhibit aflatoxin production. By combining the action of gamma radiation with humidity of the wheat (humidity 13-15%; 25% irradiation 6 kGy) an inactivation was reached. With the help of toxicologico-genetical tests (the Dominant Lethal Mutations Test, the Three Generations Test) the influence was traced of contaminated, irradiated substrates upon the health of experimental animals. It follows from the results obtained that in long-term feeding with contaminated wheat irradiated by gamma rays no positive mutagenic activity has been recorded. It allows to presume that wheat of humidity of 25% contaminated by a weakly toxigenic strain Aspergillus flavus irradiated by a dose of 6 kGy, and wheat of a humidity of 13-15%, contaminated by a strongly toxinogenic strain of Aspergillus flavus, irradiated by a dose of 6 kGy, are no genetic risk for white rats.     

Stimulation of macrophages and antitumor activity of radiodetoxified endotoxin

Lipopolysaccharide of Salmonella typhimurium was irradiated with gamma radiation at 10, 15, and 30 kGy doses. A dose of 30 kGy significantly detoxified the LPS (180 times). Mice were injected intraperitoneally with the radiodetoxified LPS, and it was found that it stimulated peritoneal macrophages as was evident from the enhancement of their acid hydrolases and cellular RNA content. Both LPS and radiodetoxified LPS exhibited antitumor activity against S180 cells in Swiss mice. Treatment with 20 micrograms/mouse of either LPS or 30 kGy LPS gave maximum survival of the mice (90%). These mice were found to resist the challenge of S180 cells (1 X 10(6)).     

Effect of Gamma-irradiation and Heat on Root-knot Nematode,Meloidogyne javanica

Effects of gamma-irradiation on the root-knot nematode Meloidogyne javanica were investigated. A dose of 7.5 kGy killed all second-stage juveniles (J2) within 1 day after treatment. Egg hatch was completely inhibited at 6.25 kGy. A bioassay on tomato measuring galling and egg production was used to determine the infectivity of irradiated J2 and J2 hatched from irradiated eggs. The J2 and eggs irradiated with a dose of 4.25 kGy did not induce galls or reproduce on tomato plants. When nematodes were exposed to combined irradiation and heat treatment, no synergistic effect on J2 or eggs was measured. Heat treatment at 49° C for 10 minutes or 20 minutes without irradiation immobilized J2 and prevented egg development. Irradiation rates needed to kill or incapacitate M. javanica were high and may be impractical as a quarantine measure.     

The effect of gamma-irradiation on the toxicity of malathion in V79 Chinese hamster cells and Molt-4 human lymphocytes.

There is growing interest in the irradiation of food and agricultural products for insect disinfestation, sprout inhibition, delayed ripening and the reduction of microbiological loads. Extensive research has been done on this process, and irradiation to a maximum dose of 10 kGy is recognized as safe by national and international regulatory agencies. The question has been raised, however, whether irradiation of pesticide residues might produce radiation products that were more toxic or less toxic than the original pesticide. To address this question, we observed the effects of 10 kGy of gamma-radiation on malathion as measured by sister-chromatid exchange (SCE), micronuclei formation, cell survival, growth rate and polyploid formation. We found no significant differences between the effects of irradiated and unirradiated malathion on any of these end-points. Polyploid formation was the most dramatic effect of both irradiated and control malathion on V79 Chinese hamster cells. Cell survival, polyploid formation and growth rate were slightly better in cells treated with irradiated malathion. In Molt-4 human lymphocyte cells, micronuclei formation was not affected by irradiated or unirradiated malathion. Compared to malathion alone, the lack of such biological effects indicates that none of the presumed radiation-induced breakdown products increased or decreased the endpoints studied. The number of SCE was consistently, but not significantly, higher in the cells treated with irradiated malathion. There were no significant differences in cell survival or micronucleus formation in the human lymphocyte cell line Molt-4 treated with irradiated or control malathion. Thus, the irradiation of the pesticide malathion to 10 kGy, a recommended upper dose for most food irradiations, does not significantly alter its toxicity in these in vitro systems.     

Effect of dose-rate and dose fractionation on radiation-induced hemolysis of human erythrocytes.

Human erythrocytes suspended in an isotonic Na-phosphate buffer, pH 7.4 (hematocrit 2%) were exposed under air to gamma radiation at a dose rates of 2.2 kGy.h-1 and 4.2 kGy.h-1. The dose-response curves for hemolysis of erythrocytes indicated that the process of hemolysis is inversely related to the dose-rate. At both dose-rates we observed a reduced level of hemolysis, when erythrocytes were irradiated with a split dose (0.4 kGy + 2.3 kGy with an interval time between the subsequent exposures from 1 to 4 h) in comparison with the same single dose (2.7 kGy). The maximal effect of fractionation was observed when the interfraction time was equal to 3.5 h. The influence of the interfraction temperature on this effect was observed. The results obtained indicate that enucleated human erythrocytes under suitable radiation conditions are capable of repairing radiation damage which leads to hemolysis.     

Gamma Radiation Effects on <Emphasis Type="Italic">Sporothrix schenckii</Emphasis> Yeast Cells

Sporotrichosis is a subcutaneous mycosis caused by Sporothrix schenckii. Zoonotic transmission to man can occur after scratches or bites of animals, mainly cats. In this study, the gamma radiation effects on yeast of S. schenckii were analyzed with a view of developing a radioattenuated vaccine for veterinary use. The cultures were irradiated at doses ranging from 1.0 to 9.0 kGy. The reproductive capacity was measured by the ability of cells to form colonies. No colonies could be recovered above 8.0 kGy, using inocula up to 10⁷ cells. Nevertheless, yeast cells irradiated with 7.0 kGy already were unable to produce infection in immunosuppressed mice. Evaluation by the FungaLight™ Kit (Invitrogen) indicated that yeast cells remained viable up to 9.0 kGy. At 7.0 kGy, protein synthesis, estimated by the incorporation of [L-³⁵S] methionine, continues at levels slightly lower than the controls, but a significant decrease was observed at 9.0 kGy. The DNA of 7.0 kGy irradiated cells, analyzed by electrophoresis in agarose gel, was degraded. Cytoplasmic vacuolation was the main change verified in these cells by transmission electron microscopy. The dose of 7.0 kGy was considered satisfactory for yeast attenuation since irradiated cells were unable to produce infection but retained viability, metabolic activity, and morphology.     

Electron-beam sterilization of laboratory animal diets--sterilizing effect of 10-MeV electrons from a linear accelerator.

Electron beam sterilization for laboratory animal diets was examined as an alternative to 60Co gamma rays. Solid, powder diets for "mice and rats" and solid diets for "rabbits and guinea pigs" which are the main products sterilized by 60Co gamma rays were irradiated with 10-MeV electrons from a linear accelerator at the Research Institute for Advanced Science and Technology, Osaka Prefecture University. At least 20 kGy was required to sterilize the samples irrespective of solid or powder diets, which was in good accordance with the results for 60Co gamma rays. Using a set dose of 30 kGy, a thickness of 45 mm for solid diets and 30 mm for powder diets could be sterilized by "one-sided" irradiation. "Dual-sided" irradiation could sterilize all the solid diets and the powder diets contained in the thicknesses of 90 mm and 75 mm, respectively. Irradiation effects of 10-MeV electrons on the nutrient quality of each diet were almost equivalent to those of 60Co gamma rays. These results suggest that commercially adopted sterilization doses for 60Co gamma rays are applicable to electron sterilization without modification if the depth-dose profile and the minimum dose of irradiated samples are precisely assessed.     

Improvement of human skin cell growth by radiation-induced modifications of a Ge/Ch/Ha scaffold

Gelatin-/chitosan-/hyaluronan-based biomaterials are used in tissue engineering as cell scaffolds. Three gamma radiation doses (1, 10 and 25 kGy) were applied to scaffolds for sterilization. Microstructural changes of the irradiated polymers were evaluated by using scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). A dose of 25 kGy produced a rough microstructure with a reduction of the porosity (from 99 to 96 %) and pore size (from 160 to 123 μm). Radiation also modified the glass transition temperature between 31.2 and 42.1 °C (1 and 25 kGy respectively). Human skin cells cultivated on scaffolds irradiated with 10 and 25 kGy proliferated at 48 h and secreted transforming growth factor β3 (TGF-β3). Doses of 0 kGy (non-irradiated) or 1 kGy did not stimulate TGF-β3 secretion or cell proliferation. The specific growth rate and lactate production increased proportionally to radiation dose. The use of an appropriate radiation dose improves the cell scaffold properties of biomaterials.     

Purification and physicochemical properties of α -amylase from irradiated wheat

α-Amylases from control and gamma-irradiated (at 0.2 and 2.0 kGy dose levels) wheat seedlings were purified to homogeneity and characterized. The molecular weight of the enzyme from a 2 kGy irradiated sample was slightly lower than that of the control; other general and catalytic properties also showed some differences. α-Amylase from the irradiated (2 kGy) sample had a narrow range of pH optimum and was inactivated faster at alkaline pH and by heat treatment than the enzyme from unirradiated wheat. A high apparent Michaelis constant (K _m) and a low maximal velocity (V_max) for the hydrolysis of soluble starch catalyzed by the enzyme from irradiated (2 kGy) wheat, suggested some modifications in the formation of the substrate α-amylase complex. Further, of the total number of amino acid residues lost on irradiation, dicarboxylic amino acids constituted the largest percentage; these structural alterations in the enzyme may be responsible for its partial inactivation. The total sugars liberated upon amylolysis of starch with the 2 kGy irradiated enzyme were lower than control, and there was accumulation of higher maltodextrins in the place of maltose.     

Sensitivity of planktonic and biofilm-associated Salmonella spp. to ionizing radiation

Salmonella enterica forms biofilms that are relatively resistant to chemical sanitizing treatments. Ionizing radiation has been used to inactivate Salmonella on a variety of foods and contact surfaces, but the relative efficacy of the process against biofilm-associated cells versus free-living planktonic cells is not well documented. The radiation sensitivity of planktonic or biofilm-associated cells was determined for three food-borne-illness-associated isolates of Salmonella. Biofilms were formed on sterile glass slides in a coincubation apparatus, using inoculated tryptic soy broth, incubated at 37 degrees C for 48 h. Resulting biofilms were 18 to 24 microm in height as determined by confocal scanning laser microscopy. The planktonic and biofilm cultures were gamma irradiated to doses of 0.0 (control), 0.5, 1.0, 1.5, 2.0 and 2.5 kGy. The D(10) value (the dose of radiation required to reduce a population by 1 log(10), or 90%) was calculated for each isolate-culture based on surviving populations at each radiation dose. The D(10) values of S. enterica serovar Anatum were not significantly (P < 0.05) different for biofilm-associated (0.645 kGy) and planktonic (0.677 kGy) cells. In contrast, the biofilm-associated cells of S. enterica serovar Stanley were significantly more sensitive to ionizing radiation than the respective planktonic cells, with D(10) values of 0.531 and 0.591 kGy, respectively. D(10) values of S. enterica serovar Enteritidis were similarly reduced for biofilm-associated (0.436 kGy) versus planktonic (0.535 kGy) cells. The antimicrobial efficacy of ionizing radiation is therefore preserved or enhanced in treatment of biofilm-associated bacteria.     

Radiation-induced effects on cefotaxime: ESR study

As an alternative to heat and gas exposure sterilization, ionizing radiation is gaining interest as sterilization process for medicinal products. Detection and dosimetry of pharmaceuticals radiosterilization is a growing concern to numerous government regulatory agencies worldwide. In this context, it is necessary to find methods distinguishing between irradiated and non-irradiated pharmaceuticals. In the absence of suitable detection methods, our attention was focused on electron spin resonance (ESR) spectrometry. A third generation cephalosporin, cefotaxime, was chosen as model; this antibiotic is a potential candidate for radiation treatment due to its thermosensitivity. While the ESR spectra of a nonirradiated sample presents no signal, a signal, dependent of the irradiation dose, is found in irradiated samples. The number of free radicals was estimated by comparing the second integral from radiosterilized samples and a diphenylpicrylhydrazyl reference. Estimation of the number of free radicals gives 1.9 × 10²⁰ radicals mol^-1 at 20 kGy. From this result, the G-value (number of radicals (100 eV)^-1) could be estimated to 0.3. Aside from qualitative detection, ESR spectrometry can be used for dose estimation. When quadratic, exponential or bi-exponential functions are applied to the variation of peak to peak amplitude vs. dose, these functions correlate well with the data. However, it is important to notice that linear function correlates well with the data for doses lower than 20 kGy. Since the radiation dose selected must be always based upon the bioburden of the products and the degree of sterility required (EN 552 and ISO 11137) 25 kGy could no longer be accepted as a “routine dose” for sterilizing a pharmaceutical. Doses from 6 kGy (ISO 11137) could be investigated and linear regression would appear to be the least expensive route to follow. The free radicals concentration appeared to not decrease during the 57 days of storage; the number generated during the irradiation allows the detection of radiosterilized cefotaxime up to two years after irradiation.     

Evaluation of the effect of gamma rays on the venom of Vipera lebetina by biochemical study

Snake bites represent a serious public health problem in many areas of the world. In Algeria, two widespread snakes are Vipera lebetina and Cerastes cerastes. Vipera lebetina venom causes local hemorrhage and necrosis, and it may lead to permanent limb loss. The principal causes of mortality after snakebites are acute renal failure and hemorrhage, which occur not only locally, at the site of the bite, but also systemically, contributing to the cardiovascular shock characteristic of severe envenomation. Gamma radiation has been shown to be effective for attenuating venom toxicity. Vipera lebetina venom was irradiated with two doses of gamma rays (1 and 2 kGy) from a 60Co source, and the venom's toxic, enzymatic, and structural properties were analyzed. Intraperitoneal injection of the irradiated venoms (100-500 microg/20 g mouse body mass) revealed a significant decrease of the toxicity. Irradiated venoms with 1 and 2 kGy doses were four and nine times less toxic, respectively, than the native venom. A biochemical characterization of in vitro enzymatic activities was performed. Vipera lebetina displayed in vitro caseinolytic, amidolytic, esterasic, coagulant, and phospholipase A2 activities. Caseinolytic, amidolytic, esterasic, and coagulative activities were reduced for the irradiated venoms; only phospholipase A2 activity was abolished in the irradiated venom with a dose of 2 kGy. The native and irradiated venoms were separated by gel filtration and electrophoresis. Chromatographic and electrophoretic profiles were drastically changed as compared with the native venom. Vipera lebetina venom detoxified by gamma rays was used for active immunization, and the presence of antibody in the immune sera was detected by ELISA. The immunogenic properties were preserved and the antisera obtained with the irradiated venoms could cross-react. Antisera were able to neutralize the toxic effect of V. lebetina native venom. These results indicate that irradiation of V. lebetina venom with a dose of 2 kGy can promote a significant detoxification, keeping the immunological properties intact.     

Effect of low dose and moderate dose gamma irradiation on the mechanical properties of bone and soft tissue allografts

The increased use of allograft tissue for musculoskeletal repair has brought more focus to the safety of allogenic tissue and the efficacy of various sterilization techniques. Gamma irradiation is an effective method for providing terminal sterilization to biological tissue, but it is also reported to have deleterious effects on tissue mechanics in a dose-dependent manner. At irradiation ranges up to 25 kGy, a clear relationship between mechanical strength and dose has yet to be established. The aim of this study was to investigate the mechanical properties of bone and soft tissue allografts, irradiated on dry ice at a low absorbed dose (18.3–21.8 kGy) and a moderate absorbed dose (24.0–28.5 kGy), using conventional compressive and tensile testing, respectively. Bone grafts consisted of Cloward dowels and iliac crest wedges, while soft tissue grafts consisted of patellar tendons, anterior tibialis tendons, semitendinosus tendons, and fascia lata. There were no statistical differences in mechanical strength or modulus of elasticity for any graft irradiated at a low absorbed dose, compared to control groups. Also, bone allografts and two soft tissue allografts (anterior tibialis and semitendinosus tendon) that were irradiated at a moderate dose demonstrated similar strength and modulus of elasticity values to control groups. The results of this study support the use of low dose and moderate dose gamma irradiation of bone grafts. For soft tissue grafts, the results support the use of low dose irradiation.     

辐照保藏豆制品的研究

豆制品用聚乙烯复合袋分装后,经4kGy、6kGy、8kGy、10kGy的^60Co γ-射线辐照,分别在5℃、25℃条件下贮藏,定期对其进行微生物、感官及营养成分指标检测。经检测分析,豆制品在一定剂量范围内辐照,效果良好,无异味,降低了微生物数量,对营养品质无不良影响,延长了货架期。研究结果表明,用6kGy～8kGy的剂量的γ射线辐照保藏豆制品效果最佳。     

The effect of gamma irradiation dose on cucumber (Cucumis sativus L.) haploid embryo production

Pollination with irradiated pollen was the only effective way for the induction of haploid embryo in cucurbits. The possibility of using lower doses of γ rays (Co⁶⁰ source) was studied. The effect of 0.2 and 0.3 kGy of rays was tested on five cucumber lines and three hybrids in the first experiment. It was found that there was hardly any difference between the total number of embryos produced by all studied forms. The highest number of isolated embryos was obtained from hybrids Gy-3 M and BxOg (111 and 188 respectively). The plant regeneration was estimated at 3.3 %. The best two lines and one hybrid were used in the second experiment to find the lowest possible dose of irradiation. The dose 0.05 kGy produced only diploid embryos and was rejected as too low. Other three doses (0.1; 0.2; and 0.3 kGy) effected embryo development in relation to the irradiation applied with the highest number obtained at the lowest dose. However the number of plants regenerated from each combination was similar. The plant regeneration in this experiment was 7.7 %. The effect of 0.1 and 0.3 kGy was tested during the next two years on one highly vigorous variety. It was confirmed that 0.1 kGy stimulated the development of higher number of haploid embryos.     

Effect of γ-irradiation on some physiochemical properties of konjac glucomannan

Konjac glucomannan (KGM) was irradiated at 5, 20, 50 and 100 kGy and the effects of γ-irradiation on some physiochemical properties of KGM were studied by using viscosimeter, colorimeter, gel permeation chromatography (GPC), Fourier transform infrared (FT-IR) spectroscopy, ultraviolet (UV) spectroscopy, thermal gravimetric (TG) analysis and scanning electron microscopy (SEM). γ-irradiation led to significant degradation of KGM according to the significant reduction of the weight-average molecular weight (M_w). The apparent viscosity of KGM decreased with increasing dose, while the viscosity stability was improved after irradiation. The colour of KGM became more intense brown with increasing dose up to 20 kGy. FT-IR spectra indicated that γ-irradiation introduced no significant changes into the structure but UV spectra showed a distinct absorption peak at about 265 nm, increasing with irradiation dose, which was attributed to the formation of carbonyl groups or double bond. High irradiation dose (100 kGy) caused a small decrease of thermal stability but presented no visible fissures or splitting of KGM granules according to the TG analysis and SEM microphotographs.     

DNA fragmentation by gamma radiation and electron beams using atomic force microscopy

Double-stranded pBS plasmid DNA was irradiated with gamma rays at doses ranging from 1 to 12 kGy and electron beams from 1 to 10 kGy. Fragment-size distributions were determined by direct visualization, using atomic force microscopy with nanometer-resolution operating in non-tapping mode, combined with an improved methodology. The fragment distributions from irradiation with gamma rays revealed discrete-like patterns at all doses, suggesting that these patterns are modulated by the base pair composition of the plasmid. Irradiation with electron beams, at very high dose rates, generated continuous distributions of highly shattered DNA fragments, similar to results at much lower dose rates found in the literature. Altogether, these results indicate that AFM could supplement traditional methods for high-resolution measurements of radiation damage to DNA, while providing new and relevant information.     

Effect of gamma radiation on the immunobiological and immunochemical properties of cholera exotoxin. I. Change in the biological activity of nonpurified cholera exotoxin as affected by ionizing radiation

Crude cholera exotoxin (filtrate toxin) was irradiated with increasing doses of gamma radiation. A significant drop in enterotoxicity, in the activity of the permeation factor and a decrease in toxicity were shown to occur as radiation doses increased. Radiation doses of 50-70 kGy were found to completely inactivate enterotoxicity in liquid toxic preparations. A higher radioresistance of dried preparations in comparison with liquid ones was registered: inactivation occurred at 150-200 kGy. Different batches of the initial filtrate toxin had varying radiosensitivity. The sterilizing effect of gamma radiation was achieved at doses of 20 kGy for liquid preparations and 30 kGy for dried preparations. During the prolonged storage of the irradiated preparations of crude toxin (the term of observation being 1.5 years) at different temperatures no reversion of toxicity was found to occur, while their immunogenic properties remained unchanged.