This could possibly explain the maintenance of adhered/attached E. coli O157:H7 populations at the initial levels when ground beef was used. Moreover, the ground beef microstructure might have minimized the motility of E. coli O157:H7, and thus, cell migration phenomena towards the stainless steel and HDPE surfaces. The same observations were not made at 15 c, where populations of attached E. coli O157:H7 were found at higher levels in TSB than in fat-lean homogenate and ground beef at the end of storage (Fig.1).