Interaction of live and dead Escherichia coli O157:H7 and fluorescent microspheres with lettuce tissue suggests bacterial processes do not mediate adherence

Aims: The goal of this study was to determine whether any specific bacterial processes ( biochemical or genetic) or cell surface moieties were required for the interaction between Escherichia coli O157: H7 and lettuce plant tissue. Methods and Results: Escherichia coli O157: H7 and Fluospheres (TM) (fluorescent polystyrene microspheres) were used in experiments to investigate interactions with lettuce. Fluospheres (TM) were used as they are a nonbiological material, of similar size and shape to a bacterial cell, but lack bacterial cell surface moieties and the ability to respond genetically. Live and glutaraldehyde-killed E. coli O157: H7 attached at levels of c. 5.8 log(10) cells per cm(2) following immersion of lettuce pieces into a suspension containing c. 8 log(10) CFU ml(-1). In a separate experiment, numbers of bacteria or Fluospheres (TM) associated with lettuce decreased by c. 1.5 log cm(-2) following a 1-min wash. Exposure times of 1 min, 1 h, or 6 h had little effect on the level of attachment for Fluospheres (TM), and live or killed cells of E. coli O157: H7 to lettuce tissue. Significance: These results indicate that bacterial processes and cell surface moieties are not required for the initial interaction of E. coli O157: H7 to lettuce plant tissue.