The Journal of Food Protection, Vol. 73, No. 10, 2010 recently published a study that sought to investigate the fate of E. coli O157:H7 applied to the surface of lettuce leaves that had either been exposed to insects that commonly infest leafy greens or that had been injured by physical abrasion. 

The study’s tests were complex, involving a variety of methods of applying the E. coli O157:H7 bacteria (innoculum) to both the abaxial (underside) and top side of spinach and lettuce leaves, including by mist and droplets, as well innoculating with differing concentrations of bacteria.  The study also includes interesting discussion on the effect that natural host (here, lettuce and spinach leaves) defenses against contamination and bacterial growth, as well as on the mechanisms (aside from mechanical abrasion or insect damage) by which E. coli O157:H7 can be internalized into the structure of a lettuce or spinach leaf.  Here are some excerpts and the study’s conclusion: