Lettuce leaves a nasty taste

Escherichia coli has been isolated with increasing frequency from fresh produce — including leaf lettuce — but the mechanisms by which the pathogen is able to enter the plants remain unclear. In January Applied and Environmental Microbiology, Ethan Solomon and colleagues from Rutgers University, New Brunswick, New Jersey, USA, show that E. coli O157:H7 can enter the plant via the root system and migrate to its leaves where it resists traditional sanitizing methods.

Solomon et al. planted lettuce in a mixture of soil and fresh cow manure inoculated with a fluorescently tagged E. coli O157:H7. At maturation, they observed that E. coli migrated to internal locations in plant tissue through the root system and could be seen throughout the edible portion of the lettuce. In addition, they demonstrated a similar transmission of the bacterium to lettuce leaves from contaminated irrigation water (Appl Environ Microbiol 2002, 68:397-400).

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