Survival and injury of Listeria monocytogenes, Listeria innocua and Listeria ivanovii in ground pork following electron beam irradiation

The sensitivity of five strains of Listeria to electron beam irradiation in ground pork as well as the extent of sublethal radiation injury exhibited by each were investigated. Ground pork was inoculated with one of five strains of Listeria and irradiated with from 0 to 1.25 kGy at 0.25 kGy intervals. Listeria innocua NADC 2841 was more radiation-resistant (D-10 = 0.638 kGy) than L. monocytogenes NADC 2045 Scott A (D-10 = 0.447 kGy), L. monocytogenes NADC 2783 (a hamburger isolate) (D-10 = 0.424 kGy), L. monocytogenes ATCC 15313 (D-10 = 0.445 kGy), and L. ivanovii NADC 3518 (D-10 = 0.372 kGy), when recovered on tryptic soy agar supplemented with 0.6% yeast extract. D-10 values for L. innocua, L. ivanovii, and L. monocytogenes ATCC 15313 were lower when cells were recovered on modified Oxford medium. These three strains were susceptible to radiation-induced sublethal injury, with the numbers of injured organisms increasing with irradiation dose. The two pathogenic strains of L. monocytogenes were not injured significantly at the dose levels used. The results show that the dose range currently being considered by the Food and Drug Administration for the irradiation of beef and pork (1.5 to 4.5 kGy) is adequate for the elimination of L. monocytogenes from pork.