Growth rates of Salmonella and Escherichia coli O157 : H7 in irradiated beef

Ground beef was irradiated to 0, 2, or 4 kGy and then inoculated with a mix ed culture of four serotypes of salmonellae or five strains of Escherichia coli O157:H7. The ground beef was stored at either 15 or 25 degreesC, and t he growth of the inoculated bacteria was monitored over time. Growth parame ters were determined for both the salmonellae and the E. coli O157:H7 using the Gompertz equation. There was no significant difference in lag phase du ration or generation time, irrespective of the dose to which the ground bee f had previously been exposed. Furthermore, the lag phase durations and gen eration times determined in this study did not differ significantly from pr eviously published values. This suggests that, although irradiation elimina tes a significant portion of the spoilage microflora in ground beef, the ab sence of this microflora provides no competitive advantage to the growth of salmonellae or E coli O157:H7 in ground beef.