Inactivation of avirulent Yersinia pestis in Butterfield's phosphate buffer and frankfurters by UVC (254 nm) and gamma radiation

Lack of correlation of desiccation and radiation tolerance in microorganisms from diverse extreme environments tested under anoxic conditions

Four facultative anaerobic and two obligate anaerobic bacteria were isolated from extreme environments (deep subsurface halite mine, sulfidic anoxic spring, mineral-rich river) in the frame MASE (Mars Analogues for Space Exploration) project. The isolates were investigated under anoxic conditions for their survivability after desiccation up to 6 months and their tolerance to ionizing radiation up to 3000 Gy. The results indicated that tolerances to both stresses are strain-specific features. Yersinia intermedia MASE-LG-1 showed a high desiccation tolerance but its radiation tolerance was very low. The most radiation-tolerant strains were Buttiauxella sp. MASE-IM-9 and Halanaerobium sp. MASE-BB-1. In both cases, cultivable cells were detectable after an exposure to 3 kGy of ionizing radiation, but cells only survived desiccation for 90 and 30 days, respectively. Although a correlation between desiccation and ionizing radiation resistance has been hypothesized for some aerobic microorganisms, our data showed that there was no correlation between tolerance to desiccation and ionizing radiation, suggesting that the physiological basis of both forms of tolerances is not necessarily linked. In addition, these results indicated that facultative and obligate anaerobic organisms living in extreme environments possess varied species-specific tolerances to extremes.

Inactivation of avirulent Yersinia pestis in beef bologna by gamma irradiation

Yersinia pestis, a psychrotrophic pathogen capable of growth at refrigeration temperatures, can cause pharyngeal and gastrointestinal plague in humans that consume contaminated foods. Because Y. pestis is listed as a select agent for food safety and defense, evaluation of food safety intervention technologies for inactivation of this pathogen is needed. Ionizing (gamma) radiation is a safe and effective intervention technology that can inactivate pathogens in raw and processed meats, produce, and seafood. In this study, we investigated the effect of temperature on the ability of ionizing radiation to inactivate avirulent Y. pestis in beef bologna. The mean (±standard error of the mean) radiation D(10)-values (the radiation dose needed to inactivate 1 log unit or 90% of the population of a microorganism) for avirulent Y. pestis suspended in beef bologna samples were 0.20 (±0.01), 0.22 (±0.01), 0.25 (±0.02), 0.31 (±0.01), 0.35 (±0.01), and 0.37 (±0.01) kGy at temperatures of 5, 0, -5, -10, -15, and -20°C, respectively. When incorporated into a three-dimensional mesh, the predictive model followed a parabolic fit (R(2) = 0.84), where the log reduction = -0.264 - (0.039 × temp) - (3.833 × dose) - (0.0013 × temp(2)) - (0.728 × dose(2)). These results indicate that ionizing radiation would be an effective technology for control of Y. pestis in ready-to-eat fine emulsion sausage products.