P1-230 Growth Behaviors of Stressed and Non-stressed Shiga Toxin-producing Escherichia coli in Ground Beef and Spinach

Sunday, July 26, 2015
Exhibit Hall (Oregon Convention Center)
Byong Kwon Yoo, U.S. Department of Agriculture-ARS, Wyndmoor, PA
Yanhong Liu, U.S. Department of Agriculture-ARS, Wyndmoor, PA
Vijay Juneja, U.S. Department of Agriculture-ARS, Wyndmoor, PA
Lihan Huang, U.S. Department of Agriculture-ARS, Wyndmoor, PA
Cheng-An Hwang, U.S. Department of Agriculture-ARS, Wyndmoor, PA
Introduction: Meat products and produce contaminated with Shiga Toxin-producing Escherichia coli (STEC) were linked to several foodborne illness outbreaks. Among the STEC, O157 and non-O157 are the two major classes implicated in the outbreaks.

Purpose: The aim of this study was to compare the growth behaviors of O157 and non-O157 STEC and determine the effects of environmental stresses on their growth in ground beef and spinach.

Methods: Stressed cells of three O157:H7 and four non-O157 (O26:H11, O103:H1, O104:H4, and O145:NM) STEC were obtained by subjecting the cells to 2 ppm chlorine, aw 0.97, pH 5, or 15-day starvation. A cocktail mix of stressed or non-stressed O157 or non-O157 was inoculated into 5 g irradiated beef or spinach and stored at 8, 12, or 16°C for 4 weeks. The cell populations during storage were compared to evaluate the growth behavior of O157 and non-O157 and the effects of stresses on their growth.

Results: At 8°C, the population of non-O157 (3.1 log CFU/g) was significantly (P < 0.05) higher than O157 (1.9 log CFU/g) in ground beef after one week, and the population difference (3.9 vs. 1.7 log CFU/g, P < 0.05) was also observed after 4 weeks. However, in spinach, the populations after 4 weeks at 8°C were not significant (3.9 vs. 3.3 log CFU/g). Starvation and chlorine stress induced better growth of non-O157 than O157 in ground beef (4.5 vs. 1.2 log CFU/g) and spinach (4.7 vs. 2.5 log CFU/g), respectively. Cell populations of stressed O157 or non-O157 STEC were not different from those of non-stressed O157 or non-O157 in beef and spinach stored at 12 and 16°C.

Significance: Results suggested that the growth behaviors of O157 and non-O157 in beef and spinach were different at 8°C, but not at 12 and 16°C. This information could also be helpful for designing temperature-abuse challenge studies concerning O157 or non-O157 STEC.