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 10(6) and 10(9) CFU L. monocytogenes per mi were suspended in tryptic soy broth and exposed to 0 to 5 key gamma radiation at 20, 4, and -80 degrees 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 degrees C but this was not true at 4 or -80 degrees C. With 1- and 2-h TBFs at 20 degrees 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.