Effect of combined heat and radiation on microbial destruction

Applied and Environmental Microbiology (Impact Factor: 3.67). 06/1977; 33(5):1170-6.
Source: PubMed


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.

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    • "There was a significant difference in D 10 values of anaerobic spore formers between the two sludge matrices (p < 0.001), However, no such difference was observed in case of aerobic spore formers (p = 0.293). Studies have been conducted in past, to assess the inactivation of B. subtilis in water and phosphate buffers using ionizing radiation (Fisher and Pflug, 1977; Monk et al., 1995; Pribil et al., 2007). It was shown that, 6.5 kGy of e-beam is required to reduce the spore population in tap water by 1 log (Pribil et al., 2007). "
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    ABSTRACT: Microbial pathogens in municipal sewage sludges need to be inactivated prior to environmental disposal. The efficacy of high energy (10MeV) e-beam irradiation to inactivate a variety of selected microbial pathogens and indicator organisms in aerobically and anaerobically digested sewage sludge was evaluated. Both bacterial and viral pathogens and indicator organisms are susceptible to e-beam irradiation. However, as expected there was a significant difference in their respective e-beam irradiation sensitivity. Somatic coliphages, bacterial endospores and enteric viruses were more resistant compared to bacterial pathogens. The current US EPA mandated 10kGy minimum dose was capable of achieving significant reduction of both bacterial and viral pathogens. Somatic coliphages can be used as a microbial indicator for monitoring e-beam processes in terms of pathogen inactivation in sewage sludges.
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    ABSTRACT: Spores of Clostridium perfringens, type A, were given separate or sequential treatments of gamma radiation (0 to 0.7 Mrad) and/or high temperature (93 to 103 degrees C). Prior heating, sufficient to inactivate 40 to 99% of the viable spores, had no effect on the subsequent radiation inactivation rate. Prior irradiation had a sensitizing effect on subsequently heated spores. The degree of sensitization to heat, as measured by thermal inactivation rate, increased with increased radiation pretreatment dose.
    Preview · Article · Oct 1978 · Applied and Environmental Microbiology
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