Food-poisoning outbreaks linked to Escherichia coli are often associated with tainted meat products but up to 30% of these are caused by people eating contaminated vegetables, and that has risen with the popularity of the organic process, as was seen in the 2011 outbreak in Europe that caused 53 deaths.
A new presentation at the Society for General Microbiology's Annual Meeting in Liverpool showed that disease-causing E. coli O157:H7 interacts directly with plant cells, allowing it to anchor to the surface of a plant, where it can multiply.
The researchers said that E. coli O157:H7 uses the flagella on its surface to penetrate the plant cell walls. The team showed that purified flagella were able to directly interact with lipid molecules found in the membranes of plant cells. E. coli bacteria lacking flagella were unable to bind to the plant cells.
Once attached, the E. coli are able to grow on, and colonize, the surface of the plant. At this point, they can be removed by washing, although the researchers showed that a small number of bacteria are able to invade inside the plant, where they become protected from washing. The group have shown that E. coli O157:H7 is able to colonize the roots of both spinach and lettuce.
Dr. Nicola Holden of the James Hutton Institute in Scotland, who led the research, said, "This work shows the fine detail of how the bacteria bind to plants. We think this mechanism is common to many food-borne bacteria and shows that they can exploit common factors found in both plants and animals to help them grow. Our long term aim is to better understand these interactions so we can reduce the risk of food-borne disease."
The researchers believe that the E. coli O157:H7 bacteria use the same method of colonizing the surface of plants as they do when colonizing the intestines of animals. The work shows that these bacteria are not simply transported through the food chain in an inert manner, but are actively interacting with both plants and animals.
While outbreaks of vegetable-associated E. coli outbreaks are rare in the UK, they do still occur, as was seen in 2013 when contaminated watercress entered the food chain resulting in seven people being hospitalized. By understanding the mechanisms of how the bacteria interact with plants, the researchers are hoping to find targeted ways to stop the binding, reducing the risk of food contamination.