Radiation Sensitivity Of Bacteria Research Articles

Effects of irradiation conditions on the radiation sensitivity of microorganisms in the presence of OH-radical scavengers

Purpose: The purpose of the paper was to investigate the protective effect of some scavengers of OH radicals (hydroxyl radicals) on the radiation sensitivity of bacteria (in some cases also yeast) under normoxic (in air) or hypoxic (suboxic) conditions and to compare the obtained results with those published earlier for the yeast, all in a wide interval of irradiation conditions. Another aim was to investigate a possible impact of the reaction order of the reaction between the scavengers and the OH radicals on the protection of the cells.Materials and Methods: In order to study the protective effect of OH scavengers we used various concentrations of methanol and potassium formate (in some cases also ethanol) in isotonic salt solutions. These solutions containing living bacteria (Escherichia coli) or yeast (Saccharomyces cerevisiae) were irradiated with 60Co radiation using various doses and dose rates. Irradiation was performed in air, in some cases under the hypoxic conditions. The number of surviving cells was determined prior to and after irradiation in suspension with and without scavengers. The surviving fractions after irradiation with and without scavenger were evaluated.Results: The surviving fraction of bacterial cells increases linearly with increasing concentration of both scavengers. The fraction of surviving cells does not increase with increasing concentration of the scavengers under suboxic conditions. The protective effect Ϭ increases linearly with increasing scavenging efficiency and this dependence is much sharper under normoxic conditions than under suboxic ones. The specific protection k is much higher for the methanol than for the potassium formate.Conclusions: The basic characteristics of the impact of scavengers of OH radicals on radiation sensitivity of both bacteria and yeast are the same in a wide interval of doses and dose rates. The specific protection effect is much higher under the normoxic conditions. This protective effect is inversely proportional to the rate constant of the reaction between the scavenger and the OH radicals. It seems to be obvious that the presence of oxygen during irradiation is a necessary condition for the protective action of the scavengers which may be partially controlled by some transport processes and may be connected with the radiation sensitivity of the cells. On the other hand, the change of the reaction order of the reaction of the scavenger with the OH radicals has turned out to be unimportant.

Radiation sensitivity of bacteria and virus in porcine xenoskin for dressing agent

In this study, gamma irradiation sensitivities of bacteria and viruses in porcine skin were evaluated to establish the optimum sterilization condition for the dressing material and a xenoskin graft. Escherichia coli and Bacillus subtilis were used as model pathogens and inoculated at 106–107logCFU/g. As model viruses, porcine parvovirus (PPV), bovine viral diarrhea virus (BVDV), and poliovirus were used and inoculated at 105–106 TCID50/g into porcine skin. The D10 value of E. coli was found to be 0.25±0.1kGy. B. subtilis endospores produced under stressful environmental conditions showed lower radiation sensitivity as D10 was 3.88±0.3kGy in porcine skin. The D10 values of PPV, BVDV, and poliovirus were found to be 1.73±0.2, 3.81±0.2, and 6.88±0.3kGy, respectively. These results can offer the basic information required for inactivating pathogens by gamma irradiation and achieving dressing material and porcine skin grafts.

Inactivation of a non-pathogenic strain of E. coli by ionising radiation

Ionising radiation is an effective method to reduce pathogenic E. coli O157:H7 in meat and poultry products. Radiation sensitivity of bacteria, however, depends on several factors. After applying an irradiation dose of 1 kGy to cultures of the non-pathogenic strain of E. coli, DSM 498, grown and irradiated in nutrient broth, reductions of 3–4 decimal units were achieved ( D 10 = 0.27 kGy). If grown on minced turkey meat, however, reduction rates were lower ( D 10 = 0.47 kGy). Even lower reduction rates were obtained during irradiation of frozen meat ( D 10 = 0.72 kGy) compared to treatments at cooling temperatures ( D 10 = 0.48 kGy). For data evaluation, both, first order reduction kinetics and the Weibull model were compared. The results emphasise the necessity to determine inactivation kinetics in food matrices of target extrinsic factors (e.g. temperature).

Radiation Sterilization of the Crude Drug "Glycyrrhiza".

The microbial contamination levels of fifteen crude drugs “Glycyrrhiza”, which had been harvested in and imported from China and Russia, and their radiation sensitivities were investigated. Specified indicator microorganisms such as Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa were not detected, and the number of bacteria and fungi adhering to those drugs were in the range 10 3-10 5cells/g and 102-105 spores/g, respectively. Those contamination levels were higher than values of the microbial limits of natural raw materials givenin The United States Pharmacopoeial Forum (1992). The average of D10 value as radiation sensitivity of bacteria and fungi to gamma rays were 2.2 and 0.98kGy, respectively. From these values, the survival doses (SD) required to attain the definitive microbial limits (bacteria, <20 CFU/g or ml; fungi, <10 CFU/g or ml) were calculated to be 7.5 kGy and 2.7 kGy. These SD values are sufficiently lower than the dose of 10 kGy allowed for food irradiation. On the other hand, the quality of Glycyrrhiza powder irradiated up to 30 kGy passed the “Crude Drugs Test”prescribed in The Japanese Pharmacopoeia Thirteenth Edition.

The effect of N-ethylmaleimide on the radiation sensitivity of bacteria.

SUMMARY: The sensitization of Escherichia coli strain B/r to γ radiation was shown to take place within a few minutes of the addition of N-ethylmaleimide. Sensitization was demonstrated with as little as 0.0001 m-N-ethylmaleimide, but a much higher concentration (> 0.002 m) was necessary for any bactericidal effect. The N-ethyl-maleimide had to be present during irradiation in order to be effective. Staphylococcus aureus and a Pseudomonas sp. but not spores of Bacillus subtilis, were also sensitized by N-ethylmaleimide. The Pseudomonas sp. was only sensitized under anoxic conditions; this may indicate that, with this organism, N-ethylmaleimide and oxygen acted competitively in enhancing radiation damage. Possible mechanisms of sensitization are discussed.

Effect of gamma-radiation on Escherichia coli grown in deuterium oxide medium.

IT has been shown by several authors, for example by Alper and Gillies1, that the nature of the growth medium has an effect on the radiation sensitivity of bacteria with regard to their ability to divide and form colonies. A simple, and yet considerable, change in the growth medium is the substitution of D2O for H2O. It was found that, on transferring cells from normal minimal medium (NH4C1 2 gm., Na2HPO4 6 gm., KH2PO4 3 gm., NaCl 3 gm., MgCl2 10 mgm., Na2SO4 26 mgm., glucose 5 gm. per litre) to the same made in 99.5 per cent D2O, the cells grew, after a long lag period, with a generation time of 4 hr. at 37° C., which is about five times the normal. Similar results were found by Borek and Rittenberg2. Such cells, after growth, must possess very considerable substitution of deuterium for hydrogen, with consequent modification of hydrogen-bonded molecular structures as well as any changes due to the increased rotational moment of inertia of water. The greatly reduced rate of division could be due to slowed enzyme kinetics, to less efficient protein synthesis, or to some modification in the DNA, among other reasons. Since it is likely that radiation action, as regards cell division, is concerned with the DNA or its organization, it seemed of interest to see whether cells grown in D2O showed any differences in radiation sensitivity.