Sensitivity of Listeria monocytogenes to irradiation

Irradiation of Listeria monocytogenes was carried out in culture media and pork meat paste at room temperature with 60Co radiation source of 6.6 kGy.h-1 dose rate. The employed doses were 0, 0.5, 1, 2, 3, 4 and 6 kGy. Because of the expected great number of injured cells, parallel to the direct counting at selective media, liquid as well as solid resuscitation methods were used. One strain of out 3 survived as high as 4 kGy irradiation. Radiation with 2 kGy resulted 7 log cycles reduction of cell count. After lower irradiation doses the L. monocytogenes count decreased in proportion to increasing doses. It has been concluded that L. monocytogenes, compared with Gram-negative pathogens, are less sensitive to irradiation.