Radiation responses of foodborne microorganisms, recovery from potentially lethal radiation damage

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Lucht, Lisa Michelle
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The ability of common foodborne microorganisms to effect repair of radiation-induced potentially lethal damage (PLD) was examined. Microbial cultures in stationary growth phase were harvested, re-suspended in phosphate buffer at 0$\sp\circ$C, and irradiated. A two stage incubation protocol was used to determine the ability of irradiated microorganisms to recover from PLD. In the first stage (recovery step) replicates of appropriate dilutions of irradiated cultures were plated onto agar plates and incubated for 20 h at specified temperatures (ranging from 2 to 37$\sp\circ$C, respectively) which are suboptimal for growth. Duration of incubation for the irradiated controls was equivalent to the sum of the two separate incubations for the groups subjected to the recovery step. The ratio of survivors assayed with and without a recovery step defined a recovery factor (RF), which reflects the ability of a particular culture to repair potentially lethal radiation damage. RF as a function of radiation dose was determined for different species of microorganisms which are of significance to t e food industry. Results of the survey indicated some microorganisms, which included Escherichia coli, Salmonella typhimurium and Brocothrix thermosphacta, show an enhanced survival attributable to the repair of PLD during the recovery step. The kinetics of repair and fixation of potentially lethal radiation damage in E. coli was also assessed using a two or three-stage incubation protocol. (Abstract shortened by UMI.)