Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/16/2002
Publication Date: 7/20/2002
Citation: Barkocy-Gallagher, G.A., Kang, D., Koohmaraie, M. 2002. Fate of field-isolated Escherichia coli O157 in ground beef at different storage temperatures. Journal of Food Protection. 65(7):1106-1109.
Interpretive Summary: E. coli O157 can cause severe disease in humans, often associated with eating undercooked ground beef. The genetic make-up of individual E. coli O157 isolates can vary; these differences may lead to differences in ability to cause disease and/or to survive ground beef processing and storage. In this study, 6 genetically-different E. coli O157 isolates were compared for their ability to survive and/or grow in ground beef stored at -20, 1, 4, and 7 deg C for up to 14 days. Five of these isolates were recently recovered from beef carcasses at processing plants and the sixth was strain ATCC 43895. At -20 deg C, each of the isolates decreased in number by the first day of storage, then their numbers largely remained unchanged through day 14. Only isolates 55AC1 and 299AB3 suffered statistically significant decreases in cell numbers. At 1 deg C, a decrease in numbers was observed at day 1 for all isolates. Two isolates, 131AC1 and 55AC1, continued to decrease in numbers after day 7, resulting in a statistically significant decrease in cell numbers by day 14 of storage. At 4 deg C, 2 isolates did not decrease in numbers by the first day of storage. However, all of the isolates increased in number by day 14 and this growth was statistically significant for isolates 114AC1, 299AB3, and ATCC 43895. At 7 deg C, all of the isolates significantly increased in number by 14 days of storage. This study shows that there are significant differences among E. coli O157 isolates in their ability to survive and/or grow at low temperatures in ground beef. This study also confirms the importance of keeping the ground beef at temperatures below 4 deg C during transportation and storage.
Technical Abstract: The survival of six Escherichia coli O157 strains, including five strains recently isolated from beef carcasses and strain ATCC 43895, was evaluated at 0, 1, 7, and 14 days in ground beef held at -20, 1, 4, and 7 deg C. At -20 deg C, the only statistically significant reductions in cell numbers occurred with strains 55AC1 and 299AB3. However, the pattern of survival at this temperature was comparable for all six E. coli O157 strains: cell numbers decreased by the first day of storage and then largely remained unchanged throughout 14 days of incubation. A similar pattern of survival occurred at 1 deg C for strains 114AC1, 237AC1, 299AB3, and ATCC 43895. Strains 131AC1 and 55AC1 experienced significant reductions of viable cell numbers by day 14 at 1 deg C, largely due to losses in cell numbers after day 7. At 4 deg C, after an initial loss of cell viability there was an increase in cell numbers by day 14 for all six strains; the increase was statistically significant for strains 114AC1, 299AB3, and ATCC 43895. When the inoculated ground beef was stored at 7 deg C, growth of all six strains was statistically significant by day 14, increasing between log10 0.9 and 1.5 CFU/g. This study demonstrates that there are significant differences in the abilities of various E. coli O157 strains to survive and grow in ground beef at cold storage temperatures. However, those differences do not appear to be attributable to recency of isolation, since strain ATCC 43895 behaved similarly to other strains. Storage temperature clearly affected growth and/or survival of varied E. coli O157 isolates, with a notable difference in growth at 1 deg C or 4 deg C.