Food-poisoning outbreaks linked to disease-causing strains of the
bacterium Escherichia coli are normally associated with tainted
meat products. However, between 20-30% of these are caused by
people eating contaminated vegetables, as was seen in the 2011
outbreak in Europe that caused 53 deaths. Research presented today
at the Society for General Microbiology's Annual Meeting in Liverpool
shows that the 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.
Researchers from the James Hutton Institute in
Scotland have identified that E. coli O157:H7 uses
whip-link structures on its surface known as flagella
-- typically used for bacterial motility -- 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
colonise, 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 colonise the roots of both
spinach and lettuce.
Dr Nicola Holden, who led the research, says: "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 colonising the surface of plants as they do when
colonising 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 as a result of strict control measures at all stages of the food
chain from plough to plate, they do still occur, as was seen in 2013
when contaminated watercress entered the food chain resulting in
seven people being hospitalised. 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.
Story Source:
The above story is based on materials provided by Society for General
Microbiology. Note: Materials may be edited for content and length.
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