Can pathogens like E. coli or Salmonella be internalized by growing fresh produce like lettuce, spinach and tomatoes?

Depends.

Researchers from the University of Delaware and the U.S. Department of Agriculture report in Foodborne Pathogens and Disease that enteric pathogens localized at subsurface sites on leafy green plant tissue prevent their removal during washing and inactivation by sanitizers. Root uptake of enteric pathogens and subsequent internalization has been a large area of research with results varying due to differences in experimental design, systems tested, and pathogens and crops used.

The potential for uptake of foodborne pathogen, both bacterial and viral, through roots into food crops is reviewed. Various factors shown to affect the ability of human pathogens to internalize include growth substrate (soil vs. hydroponic solution), plant developmental stage, pathogen genus and/or strain, inoculum level, and plant species and cultivar. Several mechanisms of internalization (“active” vs. “passive”) of bacteria to plant roots have also been hypothesized.

The authors do conclude:

• uptake through internalization is a plant–pathogen specific interaction;
• the plant growth substrate used plays a large role in the uptake of both
bacterial and viral pathogens in plants;
• intact, healthy, non-injured roots seem to discourage the uptake of bacteria cells and viruses into plants; and,
• generally, the presence of internalized pathogens in roots of plants does not directly correlate with internalized pathogens in the edible or foliar tissues of crops.

The authors also note that contaminated soil, for the most part, resulted in little to no observed internalization as compared to contaminated hydroponic solution.