Radiosensitivity of Listeria monocytogenes Using Split Dose Application of Gamma Irradiation ^†

The purpose of this study was to determine if split dose application of gamma radiation would alter the radiosensitivity of L. monocytogenes . Concentrations of 10⁶ and 10⁹ CFU L. monocytogenes per ml were suspended in tryptic soy broth and exposed to 0 to 5 kGy gamma radiation at 20, 4, and -80°C with equal split doses at 0- to 2-h time intervals (times between fractions, TBFs). Regression analyses of survival plots were used to calculate irradiation D values. Irradiation D values for split doses with 1- and 2-h TBFs were significantly lower than the control value and the values for 0.25- and 0.50-h TBFs (P < .05) at 20°C but this was not true at 4 or - 80°C With 1- and 2-h TBFs at 20°C the bacterium was near its generation time of 1.2 h, possibly accounting for the increased sensitivity. Results of this study indicated that split dose application increased the sensitivity of Listeria under certain conditions and that further investigation into this method is warranted.