ARS | Publication request: Human enteric pathogen internalization by root uptake into food crops

Submitted to: Foodborne Pathogens and Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 9, 2012
Publication Date: April 1, 2012
Citation: Hirniesen, K., Sharma, M., Kniel, K. 2012. Human enteric pathogen internalization by root uptake into food crops. Foodborne Pathogens and Disease. 9:396-405.

Interpretive Summary: Recent produce outbreaks caused by bacterial and viral foodborne pathogens has led to an examination of routes of contamination of produce crops. Internalization through root uptake of produce crops has received heightened attention since 2006, resulting in several new internalization studies conducted over the last five years. This paper analyzes and summarizes these studies addressing the internalization of bacteria and viruses through root uptake. The type of media (soil-based vs huydroponic), physical structure of roots (damaged vs. intact), and the type of crop all can affect the degree or lack of internalization of foodborne pathogens into crops: some growth conditions can promote the level of internalization in root tissues. However, although pathogens can invade the root tissues, there is little evidence for translocation (movement) to other tissues of the plant. In summary, these studies indicate that internalization through root uptake is not a significant route of contamination of produce crops. This information is useful for the fresh produce industry and government regulatory agencies.

Technical Abstract: With an increasing number of outbreaks and illnesses associated with pre-harvest contaminated produce, understanding the potential and mechanisms of produce contamination by enteric pathogens can aid in the development of preventative measures and post-harvest processing to reduce microbial populations. Enteric pathogens localized at subsurface sites on leafy green plant tissue prevent removal during washing and inactivation by sanitizers. Human pathogens are believed to enter these interior regions of the leaf through stomata, wounds or cuts, via plant pathogens or through the root system. 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 foodborne pathogen, both bacterial and viral, uptake through roots into food crops is reviewed. Various factors shown to affect the ability of human pathogens to internalize include growth medium (soil v. 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.