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

Abstract

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. Escherichia coli O157:H7 and Fluospheres (fluorescent polystyrene microspheres) were used in experiments to investigate interactions with lettuce. Fluospheres were used as they are a non-biological 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 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, and live or killed cells of E. coli O157:H7 to lettuce tissue. 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.