The genetic determinant for enhanced green fluorescent protein (EGFP) was introduced into Escherichia coli JM109 (ATCC 53323) and E. coli O157:H7 (ATCC 43895) on plasmid EGFP. The expression of EGFP did not change the growth kinetics or surface properties tested (hydrophobicity and electrophoretic mobility). Microscope slides were modified to allow for optimal viewing of thick meat samples with an inverted microscope. Two fluorescent dyes, nile red and Cy3 were used to stain for lipid and protein portions of beef muscle, respectively. Laser scanning confocal microscopy was used to observe interaction of the EGFP-expressing E. coli strains and the fluorescently stained muscle components without changing the spatial and temporal environment of the organisms.

Oil-in-water emulsions (hexadecane, minimal media [M9], and Tween 20) were used as model system to study the growth of Escherichia coli O157:H7. Stationary-phase cell density decreased as the hexadecane concentration was increased (0%, 5%, 20%, and 40% [w/v]) and biphasic growth was observed in 40% emulsions supplemented with 0.4% glucose. Thin aggregate fimbriae (curli) were observed using SEM, and a greater percentage (P < 0.001) of curli-producing colonies were isolated from 40% emulsions. Heat resistance (55 °C) of emulsiongrown cells was greater than broth-grown cells, indicating that growth and physiology under heterogeneous conditions differ from cells grown in liquid.