Towards microbiological quality assurance in radiation sterilization processing: the limiting case model applied to a microbial population having a distribution of radiation responses

A limiting case model, developed earlier to provide a conservative estimate of the proportion of non-sterile items ( P ) in an irradiated population of items contaminated with micro-organisms of a single type, has been extended to include items having organisms of different types. Estimates of P are compared with exact values derived on purely theoretical grounds and with values obtained by computer simulation of microbiological inactivation on items.     

Towards microbiological quality assurance in radiation sterilization processing: a limiting case model

A Limiting Case Model has been developed which describes the dependence on radiation dose of the proportion of items, in a population of items subjected to irradiation, which are contaminated by one or more organisms. This model is independent of the initial distribution of numbers of micro-organisms on items and represents a conservative approach to estimation of the proportions of non-sterile items in an irradiated population of items.     

A systemic model of the reproductive death of mammalian cells. The effect of radiation dose rate and fractionation

On the basis of the previously developed systemic model a study was made of the effect of dose rate on the survival of mammalian cells, RBE of small doses of heavy ions, and fractionation of radiation. There was a good agreement between theoretical and experimental results. The calculations showed that D10 (10% survival dose) is a function of dose rate P even for such ions as helium and boron which, however, exhibited an insignificant dependence of D10 on P (within the range from (10(-1) to 1 cGy/min). The influence of repair and the rate of cell division on RBE of radiation was determined.     

Activation of poly(ADP-ribose)-polymerase inhibits apoptosis of thymocytes, caused by short-wave ultraviolet radiation

The effect of (i) aphidicolin, a specific inhibitor of delta- and epsilon-polymerases, and nucleotide excision repair; (ii) 3-aminobenzamide, an inhibitor of poly(ADP-ribose) polymerase and base excision repair; and (iii) actinomycin D and cycloheximide, inhibitors of protein and RNA synthesis, respectively, on the induction of suppression of apoptosis of rat thymocytes by different doses of short-wavelength ultraviolet radiation was studied by flow cytometry. 3-Aminobenzamide suppressed the inhibition of apoptosis induced by the doses of short-wavelength ultraviolet radiation higher than 20 J/m2, increasing the cell death to a maximum. Thus, the inhibition of apoptosis by high short-wavelength ultraviolet radiation doses depends on the status of poly(ADP-ribose) polymerase and is prevented by 3-aminobenzamide. As opposed to 3-aminobenzamide, aphidicolin did not affect the cell death at short-wavelength radiation doses higher than 10 J/m2 but induced the apoptosis of unirradiated cells and cells irradiated with short-wavelength ultraviolet radiation doses lower than 10 J/m2. The inhibitors of protein and RNA synthesis cycloheximide and actinomycin D prevented the induction of apoptosis caused by low and medium doses but did not abolish the apoptosis-inhibiting activity of high doses of short-wavelength ultraviolet radiation.     

Towards microbiological quality assurance in radiation sterilization processing: simulation of the radiation inactivation process

A method is developed for computer simulation of the inactivation of microorganisms on items by irradiation. It is shown that in a population of items subjected to increasing doses of radiation the proportion contaminated approaches the appropriate Limiting Case, outlined in a previous paper, as numbers of organisms are decreased by inactivation. The behaviour of populations of items having different proportions of 'spikes' (high bioburden levels) is considered.     

Accumulation, activation and interindividual variation of the epidermal TP53 protein in response to ionizing radiation in organ cultured human skin

In this study, we examined effects of low-dose ionizing radiation on organ cultured human foreskin and, in particular, on the epidermis. Diagnostic, therapeutic, natural environmental and incidental exposures to moderate to low doses of radiation are inevitable and, although information on cultured cells continues to accumulate, little is known about the effects of low-dose radiation on human tissues. Our hypothesis is that ex vivo organ cultured foreskin is a simple and reliable model to study the biochemical effects of low-dose radiation exposure on skin. A model such as this will aid in the identification and quantification of low-dose radiation-induced changes in proteins in human skin and may be useful in the development of a precise, non-invasive, and reliable assay of exposure. In this work, several aspects of skin responses to culture conditions and radiation were examined. The responses of epidermal TP53 from organ cultured skin irradiated in medium with and without serum were found to be similar. TP53 levels in organ cultured neonatal foreskin epidermis were then examined for baseline TP53 expression. After an initial increase at 4 h, the TP53 D01 signal returned to low steady-state levels for at least 72 h. Irradiated skin samples from different individuals revealed variations in the TP53 D01 signal. The dose and temporal response of dermis and epidermis to radiation were examined by Western blotting from 0 to 24 h after exposure. After irradiation and incubation, the epidermis was removed and assayed by Western blotting and was found to have increases in the TP53 D01 epitope and the TP53 phosphoserine 15 (TP53-S15p) epitope that reached a maximum at about 3 h. In the epidermis, doses of 1-5 cGy of radiation were detectable with the TP53 D01, and CDKN1A antibodies and doses greater than 10 cGy were detectable with the TP53-S15p antibody. When the dermis was compared to epidermis, it was found that dermis had a smaller response to radiation and more phosphorylated TP53.     

Exposure to low dose of gamma radiation enhances the excision repair in Saccharomyces cerevisiae

The effect of low doses of ionizing and nonionizing radiation on the radiation response of yeast Saccharomyces cerevisiae toward ionizing and nonionizing radiation was studied. The wild-type strain D273-10B on exposure to 54 Gy gamma radiation (resulting in about 10% cell killing) showed enhanced resistance to subsequent exposure to UV radiation. This induced UV resistance increased with the incubation time between the initial gamma radiation stress and the UV irradiation. Exposure to low doses of UV light on the other hand showed no change in gamma or UV radiation response of this strain. The strains carrying a mutation at rad52 behaved in a way similar to the wild type, but with slightly reduced induced response. In contrast to this, the rad3 mutants, defective in excision repair, showed no induced UV resistance. Removal of UV-induced pyrimidine dimers in wild-type yeast DNA after UV irradiation was examined by analyzing the sites recognized by UV endonuclease from Micrococcus luteus. The samples that were exposed to low doses of gamma radiation before UV irradiation were able to repair the pyrimidine dimers more efficiently than the samples in which low gamma irradiation was omitted. The nature of enhanced repair was studied by scoring the frequency of induced gene conversion and reverse mutation at trp and ilv loci respectively in strain D7, which showed similar enhanced UV resistance induced by low-dose gamma irradiation. The induced repair was found to be essentially error-free. These results suggest that irradiation of strain D273-10B with low doses of gamma radiation enhances its capability for excision repair of UV-induced pyrimidine dimers.     

Cancer mortality risk among workers at the Mayak nuclear complex

At present, direct data on risk from protracted or fractionated radiation exposure at low dose rates have been limited largely to studies of populations exposed to low cumulative doses with resulting low statistical power. We evaluated the cancer risks associated with protracted exposure to external whole-body gamma radiation at high cumulative doses (the average dose is 0.8 Gy and the highest doses exceed 10 Gy) in Russian nuclear workers. Cancer deaths in a cohort of about 21,500 nuclear workers who began working at the Mayak complex between 1948 and 1972 were ascertained from death certificates and autopsy reports with follow-up through December 1997. Excess relative risk models were used to estimate solid cancer and leukemia risks associated with external gamma-radiation dose with adjustment for effects of plutonium exposures. Both solid cancer and leukemia death rates increased significantly with increasing gamma-ray dose (P < 0.001). Under a linear dose-response model, the excess relative risk for lung, liver and skeletal cancers as a group (668 deaths) adjusted for plutonium exposure is 0.30 per gray (P < 0.001) and 0.08 per gray (P < 0.001) for all other solid cancers (1062 deaths). The solid cancer dose-response functions appear to be nonlinear, with the excess risk estimates at doses of less than 3 Gy being about twice those predicted by the linear model. Plutonium exposure was associated with increased risks both for lung, liver and skeletal cancers (the sites of primary plutonium deposition) and for other solid cancers as a group. A significant dose response, with no indication of plutonium exposure effects, was found for leukemia. Excess risks for leukemia exhibited a significant dependence on the time since the dose was received. For doses received within 3 to 5 years of death the excess relative risk per gray was estimated to be about 7 (P < 0.001), but this risk was only 0.45 (P = 0.02) for doses received 5 to 45 years prior to death. External gamma-ray exposures significantly increased risks of both solid cancers and leukemia in this large cohort of men and women with occupational radiation exposures. Risks at doses of less than 1 Gy may be slightly lower than those seen for doses arising from acute exposures in the atomic bomb survivors. As dose estimates for the Mayak workers are improved, it should be possible to obtain more precise estimates of solid cancer and leukemia risks from protracted external radiation exposure in this cohort.     

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.     

Effect of Ionizing Radiation on Immunity

Ionizing radiation has a deleterious effect on the immunity mechanism, particularly when large but sublethal doses are applied over a short period of time. The hematopoietic system is extremely sensitive, and a fall in the lymphocytes is one of the most characteristic manifestations. The normal balance of the microflora of the intestinal and respiratory tracts is disturbed, which results in a bacteremia and may lead to death of the host. Active immunity is seriously interfered with if the irradiation occurs shortly before the injection of an antigen. There is also reduced resistance to pathogenic micro-organisms, which may lead to fatal infections. Prolonged irradiation at low levels does not seem to affect immunity adversely. Active immunization should be carried out well in advance of exposure to radiation, and supportive treatment commenced immediately after exposure to large doses.     

Quality Assurance of Sterilized Products: Verification of a Model Relating Frequency of Contaminated Items and Increasing Radiation Dose

Values of the y -radiation resistance parameters ( k and n of the 'multi-hit' expression) for Bacillus pumilus E601 spores and Serratia marcescens cells have been determined and the constancy of values for a given test condition demonstrated. These organisms, differing by a factor of about 50 in k value, have been included in a laboratory test system for use in verification of a model describing the dependence of the proportion of contaminated items in a population of items on radiation dose. The proportions of contaminated units of the test system at various y-radiation doses have been measured for different initial numbers and types of organisms present in units either singly or together. Using the model, the probabilities of contaminated units for corresponding sets of conditions have been evaluated together with associated variances. Measured proportions and predicted probabilities agree well, showing that the model holds in a laboratory contrived situation.     

Risk of second primary thyroid cancer after radiotherapy for a childhood cancer in a large cohort study: an update from the childhood cancer survivor study

Previous studies have indicated that thyroid cancer risk after a first childhood malignancy is curvilinear with radiation dose, increasing at low to moderate doses and decreasing at high doses. Understanding factors that modify the radiation dose response over the entire therapeutic dose range is challenging and requires large numbers of subjects. We quantified the long-term risk of thyroid cancer associated with radiation treatment among 12,547 5-year survivors of a childhood cancer (leukemia, Hodgkin lymphoma and non-Hodgkin lymphoma, central nervous system cancer, soft tissue sarcoma, kidney cancer, bone cancer, neuroblastoma) diagnosed between 1970 and 1986 in the Childhood Cancer Survivor Study using the most current cohort follow-up to 2005. There were 119 subsequent pathologically confirmed thyroid cancer cases, and individual radiation doses to the thyroid gland were estimated for the entire cohort. This cohort study builds on the previous case-control study in this population (69 thyroid cancer cases with follow-up to 2000) by allowing the evaluation of both relative and absolute risks. Poisson regression analyses were used to calculate standardized incidence ratios (SIR), excess relative risks (ERR) and excess absolute risks (EAR) of thyroid cancer associated with radiation dose. Other factors such as sex, type of first cancer, attained age, age at exposure to radiation, time since exposure to radiation, and chemotherapy (yes/no) were assessed for their effect on the linear and exponential quadratic terms describing the dose-response relationship. Similar to the previous analysis, thyroid cancer risk increased linearly with radiation dose up to approximately 20 Gy, where the relative risk peaked at 14.6-fold (95% CI, 6.8-31.5). At thyroid radiation doses >20 Gy, a downturn in the dose-response relationship was observed. The ERR model that best fit the data was linear-exponential quadratic. We found that age at exposure modified the ERR linear dose term (higher radiation risk with younger age) (P < 0.001) and that sex (higher radiation risk among females) (P = 0.008) and time since exposure (higher radiation risk with longer time) (P < 0.001) modified the EAR linear dose term. None of these factors modified the exponential quadratic (high dose) term. Sex, age at exposure and time since exposure were found to be significant modifiers of the radiation-related risk of thyroid cancer and as such are important factors to account for in clinical follow-up and thyroid cancer risk estimation among childhood cancer survivors.     

Influence of Irradiation on the Risk of Transmission of HIV in Bone Grafts Obtained from Appropriately Screened Donors and Followed by Radiation Sterilization

We studied the effects of radiation (electrons of 6.2 MeV) at different temperatures with respect to the inactivation of the human immunodeficiency virus to determine the radiosensitivity of the virus. Using a mathematical model describing the dependence on radiation dose of the proportion of sterile items in a population of bone allografts contaminated by HIV, and subjected to irradiation, we have commented on and explained the calculation of the sterility assurance level in bone transplantation according to different doses of irradiation at different temperatures. Simultaneous application of heat and radiation increases inactivation of HIV. Given the relative imprecision of viral sensitivity curves and the impossibility of knowing the number of viral particles in a patient at a given moment of the disease, irradiation does not authorize bone transplantation without screening. However, irradiation can be considered as a serious adjuvent to decrease the risk of contamination after screening.     

Effects of UV-B radiation on growth and motility of four phytoplankton species

A depletion of the stratospheric ozone layer would result in an increased UV-B radiation, which could have harmful effects on marine organisms. The aim of this study was to determine the effects of an enhanced UV-B radiation (280–320 nin) on the motility and growth in four Swedish phytoplanklon species. The different plankton species were exposed to different doses of UV-B radiation during growth. The growth of the motile dinoflagellates, Gyronidium aureolum Hulburt (Ba 6), and Prorocentrum minimum (Pav.) P. Schiller (Ba 12), was more sensitive to UV-B radiation than the non-motile diatoms Dityhim brightwellii (P. West) Grun (Ba 15) and Phaeodactylum tricornutum Bohlin (Ba 16). One week of UV-B radiation 2 h daily (159 J m⁻² day⁻¹), had a dramatic effect on the growth of the dinoflagellates, while the diatoms were nearly unaffected. On the other hand, when given higher intensity of UV-B radiation (312, 468 and 624 J m⁻² day⁻¹) during the initial phase of growth, also the growth of the diatom, D. brightwellii, was inhibited. Not only the growth but also the swimming speed of the dinoflagellates C. aureolum and P. minimum were affected by UV-B radiation. The speed decreased rapidly after 1–2 h of UV-B radiation (312 J m⁻² day⁻¹), and after longer irradiation times the dinoflagellates lost their motility. G. aureolum exposed to UV-B radiation, regained normal speed after two weeks of visible light.     

Differential stimulation of an arid-environment winter ephemeral Dimorphotheca pluvialis (L.) Moench by ultraviolet-B radiation under nutrient limitation

A South African winter ephemeral D. pluvialis was exposed, under low and high nutrient conditions, to four different daily doses of biologically effective UV-B radiation. These simulated different depletions (range 0–30%) in the ozone layer at the southerly distribution limit (33° 56′S) of this species, and included daily UV-B doses received at the northerly distribution limit (26° 38′S) without ozone depletion. Growth inhibition by increased UV-B radiation was observed during early vegetative stages, but only under low nutrient conditions. Thereafter, net CO₂ assimilation rate, growth and reproduction were stimulated by an increase in UV-B radiation, though doses above those approximating a 20% ozone depletion appeared to be inhibitory. Differential stimulation occurred in the two nutrient treatments. Under high nutrient conditions, photosynthesis (specifically carboxylation efficiency), and numbers of leaves, inflorescences and diaspores per plant, and leaf areas increased, but leaf thickness decreased with increased UV-B radiation. Under low nutrient conditions, dry masses of leaves, stems, inflorescences and diaspores, and total above-ground dry masses increased with increased UV-B radiation. Foliar organic carbon and nitrogen concentrations and foliar concentrations of UV-B absorbing compounds were unaffected by increased UV-B radiation, but foliar P concentrations declined. Diaspore viability declined with increased UV-B radiation. The net effect was a 35 to 43% reduction in viable diaspore production under high nutrient conditions at UV-B doses equivalent to those currently received at the northerly distribution limit during the reproductive phase. It is concluded that anticipated increases in UV-B radiation could reduce regeneration success, and seedling survival in areas of low soil fertility, particularly at lower latitudes, and consequently increase the risk of localized population extinctions from stochastic causes.     

A monomer-dimer model explains the results of radiation inactivation: binding characteristics of insulin receptor purified from human placenta

The technique of radiation inactivation has been used on highly purified human placental insulin receptor in order to determine the functional molecular size responsible for the insulin binding and to evaluate the "affinity regulator" hypothesis, which has been proposed to explain the increase in specific insulin binding to rat liver membranes observed at low radiation doses [Harmon, J. T., Hedo, J. A., & Kahn, C. R. (1983) J. Biol. Chem. 258, 6875-6881]. Three different types of inactivation curves were observed: (1) biphasic with an enhanced binding activity after exposure to low radiation doses, (2) nonlinear with no change in binding activity after exposure to low radiation doses, and (3) linear with a loss in the binding activity with increasing radiation exposures. A monomer-dimer model was the simplest model that best described the three types of radiation inactivation curves observed. The model predicts that an increase in insulin binding activity would result after exposure to low radiation doses when the initial dimer/monomer ratio is equal to or greater than 1 and a monomer is more active than a dimer. The monomer size of the binding activity was estimated to be 227,000 daltons by this model. This value most likely reflects the size of the monomeric alpha beta form. To substantiate this model, the purified receptor was fractionated by Sepharose CL-6B chromatography. The insulin binding profile of this column indicated two peaks.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effect of substrate on the radiation resistance of yeasts isolated from sausage meat

J.-A, McCARTHY AND A.P. DAMOGLOU. 1996. The radiation resistance of a selection of yeasts isolated from sausages was assessed in phosphate-buffered saline and in sausage meat. The yeasts Candida zeylanoides, Debaryomyces hansenii and Trichosporon cutaneum exhibited sigmoidal survival curves in both substrates whilst the more sensitive Sporobolomyces roseus exhibited an exponential survival curve in buffer but a sigmoidal curve in meat. Irradiating C. zeylanoides, D. hansenii and T. cutaneum in sausage meat changed the shape of their survival curves to significantly alter the calculated parameters D _s (the dose in kGy that must be achieved before reduction in numbers occurs) and D ₁₀^sig(the dose in kGy required after the shoulder to achieve a 1 log cycle reduction in numbers). The D _s values were reduced while higher D ₁₀^sigvalues were obtained demonstrating that the sausage meat contributed a protective effect to these yeasts at higher irradiation doses. For the yeast S. roseus , similar numbers of survivors were recovered from both substrates at initial low irradiation doses (0–0.5 kGy) with the protective effect being demonstrated again at higher doses (> 2 kGy). These findings should be considered when defining a commercial process to reduce the numbers of yeasts in these products.     

Microbial monitoring of the influence of the stabilization degree of sludge when applied to soil

The aim of this study was to establish the degree of stabilization of sludge and its influence on the evolution of total aerobic micro-organisms and those of faecal origin when the sludge is applied to soil. Two different sludges were used, from a food industry (D) and from an urban treatment plant, (E). Both sludges were stabilized aerobically in laboratory conditions. The stabilization process was monitored by following the evolution of pathogenic micro-organisms and the content of total solids and volatile matter in suspension, while on the other hand the microbial evolution of the samples of soil plus sludge and control soil (S) were monitored over an incubation period of 80 days. After 20 or 40 days of incubation, in both sludge treatments the populations of pathogenic micro-organisms of faecal origin were below detectable limits, regardless of the degree of stabilization of the sludge. Soil without sludge treatment did not show pathogenic micro-organisms.     

Interactions of Candida albicans with other Candida spp. and bacteria in the biofilms

AIMS: To study the interactions between Candida albicans and 12 other species of Candida and bacteria in biofilms. METHODS AND RESULTS: The number of cells within growing biofilms in a polystyrene tube model was measured after adding C. albicans to preformed biofilms of other micro-organisms and vice versa. It was also measured after simultaneous biofilm formation of C. albicans and other micro-organisms. The number of cells of C. albicans within the growing biofilms decreased significantly (P < 0.05) when the fungus was added to preformed biofilms of Candida spp. and bacteria except, with C. parapsilosis, Torulopsis glabrata and the glycocalyx producer Pseudomonas aeruginosa. When C. parapsilosis, Staphylococcus epidermidis (nonglycocalyx producer) or Serratia marcescens was added to preformed biofilms of C. albicans, the number of cells of these micro-organisms increased in the growing biofilms. CONCLUSIONS: Biofilms of C. albicans are capable of holding other micro-organisms and more likely to be heterogeneous with other bacteria and fungi in the environment and on medical devices. SIGNIFICANCE AND IMPACT OF THE STUDY: Recognition of the heterogeneity of biofilm-associated organisms can influence treatment decisions, particularly in patients who do not respond to initial appropriate therapy.