Inactivation of Shiga Toxin-Producing Escherichia coli in lean ground beef by gamma irradiation

• The STEC D10 ranged from 0.16 to 0.48 kGy in lean ground beef.
• The mean D10 of STEC associated with human illness was 0.27 kGy.
• The mean D10 of STEC not associated with human illness was 0.36 kGy.

In this study the radiation resistance of 40 Shiga Toxin-Producing Escherichia coli (STEC) isolates which contained various combinations of the shiga toxin 1 (stx1), shiga toxin 2 (stx2), intimin (eae), and hemolysin (ehx) genes were determined. The STEC were suspended in lean ground beef and irradiated at 4 °C. D10 values, the radiation dose needed to reduce 1 log (90%) of a microorganism, ranged from 0.16 to 0.48 kGy, with a mean of 0.31 kGy for the 40 isolates. Isolates associated with illness outbreaks had a mean D10 of 0.27 kGy, while non-outbreak isolates had a mean D10 of 0.36 kGy (p < 0.05). The presence or absence of stx1, stx2, or both stx1 and 2 had no affect on D10 (p > 0.05). The presence (0.30 kGy) or absence (0.35 kGy) of ehx had no affect on D10 (p > 0.05). However, the mean D10 of isolates lacking eae (0.37 kGy) were significantly higher than those containing eae (0.27 kGy) (p < 0.05). There was no difference in D10 for isolates lacking eae regardless of whether or not they were associated with a foodborne illness outbreak (p > 0.05). It may be possible to use some of the STEC isolates which lacked eae, ehx, or both (D10 > 0.30) as avirulent surrogates in food irradiation research. The data presented in this study provides risk assessors data for metagenomic analysis as well as food and radiation processors with valuable information to control of STEC in meat.