Use of low-dose irradiation to evaluate the radiation sensitivity of Escherichia coli O157:H7, non-O157 verotoxigenic Escherichia coli, and Salmonella in phosphate-buffered saline.

Verotoxigenic Escherichia coli (VTEC) and Salmonella are major foodborne pathogens, but very little information is available on the radiation resistance of a sufficiently diverse group of these pathogens. The objective of this study was to evaluate the sensitivity of E. coli O157:H7, non-O157 VTEC, and Salmonella to a low-dose ionizing radiation treatment. Test organisms were 6 serovars of Salmonella, 5 strains of E. coli O157:H7, and 27 strains of non-O157 VTEC (representing 19 serotypes). Decimal reduction doses (D-values) for individual strains were determined in phosphate-buffered saline using an X-ray source. The viability of the bacterial cells declined with an increase in absorbed dose from 0 to 0.3 kGy. The more resistant test strains were screened at 0.5 and 0.7 kGy. All six Salmonella strains survived at 0.5 and 0.7 kGy; however, only 11 VTEC survived at 0.7 kGy. After the 0.3-kGy treatment, both E. coli O157:H7 and non-O157 VTEC had D-values with similar means and ranges (0.028 to 0.123 and 0.037 to 0.127 kGy, respectively), with no significant differences (P > 0.05). Salmonella strains had a slightly higher range of D-values (0.061 to 0.147 kGy) and a mean D-value that was significantly higher (P > 0.05) than that of both the E. coli O157:H7 and non-O157 VTEC groups.