Effect of combined heat and radiation on microbial destruction.

A series of experiments at several levels of relative humidity and radiation dose rates was carried out using spores of Bacillus subtilis var. niger to evaluate the effect of heat alone, radiation alone, and a combination of heat and radiation. Combined heat and radiation treatment of microorganisms yields a destruction rate greater than the additive rates of the independence agents. The synergistic mechanism shows a proportional dependency on radiation dose rate an Arrhenius dependency on temperature, and a dependency on relative humidity. Maximum synergism occurs under conditions where heat and radiation individually destroy microorganisms at approximately equal rates. Larger synergistic advantage is possible at low relative humidities rather than at high relative humidities.     

Effect of relative humidity of hot air on the heat resistance of Bacillus cereus spores

The heat resistance to hot air of spores of Bacillus cereus (ATCC 14579) attached to carriers of stainless steel or silicone rubber was investigated in a range from 1% to 100% relative humidity (RH). Apart from an initial stage, linear survivor curves were obtained for all relative humidities. Neither the attachment itself nor the material of the carrier had an influence on the resistance. A distinct maximum of heat resistance was found at 40% RH. At 122°C the rate constants at 40% RH were five orders of magnitude smaller than at 100% RH and two orders of magnitude smaller than at 1% RH. At relative humidities of more than 40% the rate constants were strongly temperature dependent, whereas at lower relative humidities they were less temperature dependent. No significant influence of the relative humidity on the Arrhenius activation energy was found within each humidity range. The mean values were 295 kJ mol^-1 for relative humidities of 60% to 100% RH and 165 kJ mol^-1 for 1% to 20% RH. The occurrence of a maximum is ascribed to the existence of two inactivation mechanisms, the first is retarded and the second is accelerated by a reduction of relative humidity. It is assumed that the first mechanism is a protein denaturation. The second mechanism may be an oxidative process.     

A kinetic analysis of spore inactivation in a composite heat and gamma radiation environment

This paper presents the analysis of a combined environment of dry heat and gamma radiation when applied for the purpose of spacecraft sterilization. The nature of the synergistic inactivation effect of dry heat and radiation on bacterial spores is explained using a semiempirical mathematical model, and the dependence of the inactivation rate upon a temperature dependent, nonlinear function of radiation dose rate is presented. An analysis of the temperature required for a defined population reduction with a defined upper limit on radiation dose and time is described. Also discussed is the dependency of the dose required for a defined population reduction on the radiation dose rate at any selected temperature.     

Optimizing thermal and radiation effects for bacterial inactivation

The temperatures required for dry-heat spacecraft sterilization have been known to degrade heat-sensitive components. Thermoradiation, the simultaneous application of dry heat and gamma radiation, can provide the same degree of microbial inactivation as dry heat alone while substantially reducing component degradation. This is made possible by the synergistic effects produced when relatively low levels of these agents (e.g., 90 to 350 krads and 60° to 105°C) are applied simultaneously, thus permitting the use of lower temperatures and a reduced duration of heat exposure. The effects of temperature, radiation dose rate, and relative humidity on microbial inactivation during thermoradiation exposure have been established.This experimentation was supported by NASA Contract No. W-12853.     

THE EFFECT OF WATER CONTENT UPON THE RATE OF HEAT DENATURATION OF CRYSTALLIZABLE EGG ALBUMIN

1. The denaturation rate of partially dried crystallizable egg albumin is greatly decreased by decreasing its water content. 2. The temperature of denaturation, defined as the temperature at which half of the protein becomes insoluble in distilled water after a definite time of heating, is a linear function of the relative humidity with which the protein is in equilibrium. 3. By applying the Arrhenius equation it is shown that the rate of heat denaturation at a given temperature is an exponential function of the relative humidity. 4. The application of the observed relations to the analysis of the mechanism of thermal death of microorganisms is suggested. 5. The water content of native and heat-denatured egg albumin is determined as a function of the relative humidity of water vapor. It is shown that the heat-denatured modification takes up approximately 80 per cent as much water at all relative humidities as does native egg albumin.     

Thermoradiation Inactivation of Naturally Occurring Bacterial Spores in Soil

Samples of soil collected from the Kennedy Space Center near the spacecraft assembly facilities were found to contain microorganisms very resistant to conventional sterilzation techniques. The inactivation kinetics of the naturally occurring spores in soil were investigated by using dry heat and ionizing radiation, first separately and then simultaneously. Dry-heat inactivation kinetics of spores was determined at 105 and 125 C; radiation inactivation kinetics was determined for dose rates of 660 and 76 krads/h at 25 C. Simultaneous combinations of heat and radiation were then investigated at 105, 110, 115, 120, and 125 C, with a dose rate of 76 krads/h. Combined treatment was found to be highly synergistic, requiring greatly reduced radiation doses to accomplish sterilization of the population.     

Thermal interaction between animal and microclimate: a comprehensive model

An equation based on heat transfer theory is developed to predict the rate of heat loss from a homeothermic vertebrate to the environment, specified by the air temperature, humidity, windspeed and radiation receipt. The analysis incorporates the animal's thermoregulatory responses--sweating ability, vasomotor action, and regulation of body-core temperature, metabolic and respiratory rate. The loss of heat and water vapour from cattle is used as an illustration, and particular attention is given to their heat balance in hot environments. The predicted rates of heat loss from cattle indoors at various air temperatures and humidities are consistent with experiments. Outdoors, intercepted solar radiation can reduce substantially heat loss through the body tissue when the air temperature is low. In contrast, at high air temperatures the heat dissipation may not be sensitive to the radiation load, although body-core temperature is. Increased rates of air movement can aggravate strain at low air temperatures, but mitigate strain in a hot environment.     

Covalent DNA-protein crosslinking occurs after hyperthermia and radiation

Covalent DNA-protein crosslinks occur in exponentially growing mouse leukemia cells (L1210) after exposure to ionizing radiation. The amount of DNA-protein crosslinks as measured by a filter binding assay is dose dependent upon X irradiation. Although hyperthermia and radiation in combination are synergistic with respect to cell lethality, the combination does not result in an increase of DNA-protein crosslinks when assayed immediately following treatments. Hyperthermia (43 degrees C/15 min) given prior to radiation does not alter the radiation dose dependency of the amount of initial crosslinking. In addition, the amount of DNA-protein crosslinking produced by heat plus radiation is independent of the length of heating the cells at 43 degrees C. The DNA-protein crosslinks produced by 50-Gy X ray alone are removed after 2 hr at 37 degrees C. However, if hyperthermia (43 degrees C/15 min) is given prior to 100-Gy X ray, the removal of DNA-protein crosslinks is delayed until 4.0 hr after radiation. Phospho-serine and phospho-threonine bonds are not produced with either radiation or the combination of hyperthermia plus radiation as judged by the resistance of the bonds to guanidine hydrochloride. However, hyperthermia plus radiation causes an increase in phosphate to nitrogen type bonding. These results show that radiation alone causes covalent DNA-protein crosslinks. Hyperthermia in combination with radiation does not increase the total amount of the crosslinks but delays the removal of the crosslinks and alters the distribution of the types of chemical bonding. These data suggest that the synergistic action on hyperthermia with radiation is more related to the rate of removal and the type of chemical bonding involved in the covalent DNA-protein crosslinks rather than the amount of DNA-protein crosslinks.     

Effects of Environmental Factors on the Survival of Airborne T-3 Coliphage

Experiments were conducted to determine the effects of storage temperatures, relative humidity, and additives on the survival of aerosolized Escherichia coli phage T-3. The aerosol stability of the coliphage, calculated as per cent recovery, was not affected by storage at 10 or -70 C for up to 4 months. However, an increase in aerosol decay rate of coliphage stored at 10 C was observed. The effect of humidities ranging from 20 to 90% relative humidity was studied, and it was observed that humidities lower than 70% relative humidity significantly reduce the survival of airborne coliphage. The effect of various compounds on the aerosol decay rate of T-3 coliphage was studied at 50 and 85% relative humidity. Addition of dextrose in 0.1 M concentrations to the disseminating fluid significantly reduced aerosol decay rate at 50% relative humidity without affecting the decay at 85%. Addition of spermine, spermidine-phosphate, thiourea, galacturonic acid, and glucosaminic acid, individually or in combination, had no effect on aerosol decay rates. The use of deuterium oxide as the suspending fluid for dissemination had no effect on aerosol stability of the coliphage.     

Influence of shell colour on the mortality rate of the land snail Arianta arbustorum under different microclimatic regimes

The mortality of phenotypic shell colour morphs and age classes of the snail Arianta arbustorum in several microclimatic conditions was recorded. An analysis of variance was performed on five factors: adaptation temperature, relative humidity, shell colour, age class and test temperature. There were no significant differences in the mortality between different adaptation temperatures or relative humidities, but the interaction of these two factors was highly significant. There were significant differences in mortality rate between test temperature and age class. The mortality of the brown morph was higher than the yellow one at all adaptation temperatures (overall, P < 0.05). There were no significant differences between the mortality rates of the two morphs at different relative humidities. The mortality of the brown morph was higher than that of the yellow at six out of seven test temperatures. Juvenile snails survived significantly better than adults at all test temperatures.     

Influence of temperature and humidity on insecticidal effect of three diatomaceous earth formulations against larger grain borer (Coleoptera: Bostrychidae)

Laboratory experiments were carried out to evaluated three diatomaceous earth (DE) formulations--Protect-It, PyriSec (at dose rates 500, 1000, and 1500 ppm), and DEA-P (at dose rates 75, 150, and 500 ppm)--against the larger grain borer, Prostephanus truncatus (Horn) (Coleoptera: Bostrychidae), adults in stored maize, Zea mays L., at three temperatures (20, 25, and 30 degrees C) and two relative humidity (RH) levels (55 and 75%). At these conditions, the capability of progeny production in the treated substrate also was assessed. Adult survival was high, at all doses of Protect-It and PyriSec. Progeny production was also high. In contrast with the other two DEs, DEA-P was highly effective and caused complete mortality to the exposed P. truncatus adults, even at the lowest dose rate (75 ppm). In addition, progeny production was completely suppressed. Generally, Protect-it and PyriSec were more effective at 20 degrees C than at 30 degrees C. In contrast, the efficacy of DEA-P was continuously high in all temperatures and relative humidities examined.     

Pinus Halepensis and Quercus Ilex Terpene Emission as Affected by Temperature and Humidity

The short-term relationships of monoterpene emission with temperature and relative humidity were studied in Pinus halepensis L. and Quercus ilex L. seedlings grown in air-conditioned chamber. In P. halepensis terpene emission rate increased with temperature (from 15 to 35 °C) and relative humidity (from 40 - 60 to 65 - 95 %). In Q. ilex, a terpene non-storing species, it increased with temperature only at high relative humidities but not at relative humidities lower than 60 %. This revised version was published online in July 2006 with corrections to the Cover Date.     

Heat Resistance of Bacillus Spores at Various Relative Humidities

The thermal resistance characteristics of spores from strains of five different Bacillus species were determined in phosphate buffer and at relative humidities ranging from <0.001 to 100% in a closed-can system. Spores tested in the closed-can system showed a marked increase in heat resistance over those in phosphate buffer, with the greatest increases occurring at relative humidities between 1 and 50%. When estimates of the time to reduce the initial spore concentration 99.99% (F value) at eight different relative humidities were plotted against temperature, three different types of heat resistance profiles were obtained, with maximum resistances at relative humidities of 1, 7, and 30%. When the various strains of spores were heated at the relative humidity of their maximum heat resistance, their relative order of heat resistance was different from that seen in buffer. Spores from the soil isolate were most resistant under these conditions (F_121.1 = 99.5 h).     

Virus survival as a seasonal factor in influenza and poliomyelitis

Summary The influence of temperature and humidity on the survival of airborne viruses was studied in a static system. Preliminary experiments with a bacteriophage showed that relative humidity was more important than temperature and absolute humidity. The effect of relative humidity was not dependent on the composition of the medium surrounding the virus particles. The survival of influenza and poliomyelitis virus are sharply influenced by relative humidity but in an opposite way. Influenza virus survives much better at lower humidities, poliomyelitis virus at higher humidities. In countries with moderate climates the period of increasing morbility for influenza, in winter, coincides with indoor conditions of relative humidity which are optimal to virus survival. For poliomyelitis the same is true during summer (Fig. 7). Indoor relative humidity is considered an important “seasonal factor” in the epidemiology of poliomyelitis and influenza and probably of other diseases.     

Degradation of biochemical activity in soil sterilized by dry heat and gamma radiation.

The activities of three enzymes present in soil, phosphatases, urease, and decarboxylase, were monitered as indicators of the loss of biochemical information occurring when soil was sterilized by dry heat (0.08% relative humidity), gamma radiation, or a combination of both. More enzymatic activity was retained in soil sterilized by a long exposure to dry heat at relatively low temperature (8 weeks at 100.5 degrees C) than by a shorter exposure to a higher temperature (2 weeks at 124.5 degrees C). No enzymatic activity was detectable in soil sterilized by an even higher temperature (4 days at 148.5 degrees C). Soil sterilized with 7.5 Mrads of radiation retained much higher enzymatic activity than with heat sterilization. Combining sublethal doses of heat radiation effectively sterilized the soil and yielded enzymatic activities higher than those of soil sterilized by dry heat alone but lower than those of soil sterilized by radiation.     

Survival of Botrytis cinerea in Soil in South-Eastern Spain

The survival of Botrytis cinerea in sterile and unsterile soil at different temperatures and relative air humidities was investigated in south‐eastern Spain. Conidia survived only 7 days at 40^°C but, depending on relative humidity, for 30–90 days at 22^°C. High air humidity (95%) was needed to maintain soil humidity (8%) at a level that favoured conidial survival. Conidia survived better in sterile soil than in unsterile soil, probably because of the presence in the latter of soil microorganisms antagonistic to B. cinerea. Survival of conidia in environmental conditions simulating those in a greenhouse was less than 28 days. Results showed that B. cinerea conidia cannot survive over summer in south‐eastern Spain, and other primary sources of inocula are discussed.     

Degradation of biochemical activity in soil sterilized by dry heat and gamma radiation

The activities of three enzymes present in soil, phosphatases, urease, and decarboxylase, were monitered as indicators of the loss of biochemical information occurring when soil was sterilized by dry heat (0.08% relative humidity), gamma radiation, or a combination of both. More enzymatic activity was retained in soil sterilized by a long exposure to dry heat at relatively low temperature (8 weeks at 100.5°C) than by a shorter exposure to a higher temperature (2 weeks at 124.5° C). No enzymatic activity was detectable in soil sterilized by an even higher temperature (4 days at 148.5° C). Soil sterilized with 7.5 Mrads of radiation retained much higher enzymatic activity than with heat sterilization. Combining sublethal doses of heat radiation effectively sterilized the soil and yielded enzymatic activities higher than those of soil sterilized by dry heat alone but lower than those of soil sterilized by radiation.     

Crystallization kinetics of amorphous lactose, whey-permeate and whey powders

Amorphous lactose, whey-permeate and whey powders have been converted to their crystalline forms by exposure to air at various temperatures and relative humidities. The total time required for sorption, induction and crystallization of these powders was observed by following the time-dependent mass change of the powders during treatment. These experiments have shown that higher temperatures and relative humidities lead to shorter crystallization times. Lactose crystallizes within 1 min at an air temperature of 100 degrees C and relative air humidity of 80%, whereas whey-permeate and whey powders requires up to 5 min at the same set of conditions. Thus, as previously described, the presence of proteins and salts in the whey-permeate and whey powders reduces the crystallization rate. The rate constants and activation energies have been determined over a range of temperatures and humidities to enable the calculation of crystallization times for the design of an industrial process that crystallizes whey and whey-permeate powders. Finally, the crystallization rates found in this work are sufficiently fast to be applicable in an industrial process that crystallizes whey and whey-permeate powders.     

Evidence of a maternal effect that protects against water stress in larvae of the American dog tick, Dermacentor variabilis (Acari: Ixodidae)

We report that the ability to absorb water vapor from the air in larvae of the American dog tick, Dermacentor variabilis, changes depending upon moisture conditions where the eggs develop. When development occurs at lower relative humidities, resultant larvae can replenish water stores, maintain water balance, and survive at relative humidities as low as 75-85% RH, a range that agrees with previously published values for the critical equilibrium humidity or CEH. In contrast, exposure to high relative humidity conditions during development elevates the CEH to 93-97% RH. These larvae can survive only at relative humidities that are close to saturation, as 93% RH is a dehydrating atmosphere. For these larvae, absorption at 97% RH can be prevented by blocking the mouthparts with wax, indicating that an upward shift has occurred in the moisture threshold where the active mechanism for water vapor absorption operates. Based on transfer experiments between low and high relative humidities, the CEH of larvae is determined by the relative humidity experienced by the mother rather than the moisture conditions encountered by eggs after they are laid. The fact that no changes in body water content, dehydration tolerance limit and water loss rate were observed implies that adjustments to the CEH conferred by the mother have the adaptive significance of enabling larvae to maintain water balance by limiting the range of hydrating atmospheres.     

Thermoregulation by rhesus monkeys at different absolute humidities

The effect of relative humidity on thermoregulation has been well examined. Because the same relative humidity represents very different absolute humidities at different ambient temperatures, the present study was designed to examine the interaction of temperature and absolute humidity on the thermal balance of rhesus monkeys, Macaca mulatta. Thermal balance was examined in six unacclimated, unanesthetized, female rhesus monkeys at ambient temperatures of 25, 30, 35, and 40 °C and absolute humidities of 6, 22, and 40 torr. Monkeys were capable of achieving thermal balance under all conditions except at 40 °C with 40 torr absolute humidity, where experiments were stopped after rectal temperature exceeded 40.5 °C. At 40 °C, monkeys increased evaporative heat loss through both respiration and sweating; the slope of the relationship between evaporative heat loss and core temperature was attenuated by increases in absolute humidity. In contrast, absolute humidity had no direct effect on metabolic rate. The rise in body temperature under the conditions of high heat/high humidity was therefore most attributable to humidity-dependent decreases in evaporative heat loss.Abbreviations E_tot total evaporative heat loss - HR heart rate - K thermal conductance - M metabolic rate - RQ respiratory quotient - T_c core temperature - T_sk mean skin temperature - VCO₂ carbon dioxide production - VO₂ oxygen consumptionCommunicated by G. Heldmaier