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Pathogens Thrive on Ripe Fruit, Dublin Conference Learns

Escherichia coil and Salmonella enterica thrive on ripe fruit, according to research presented at the Society for General Microbiology’s Spring Conference held last week in Dublin.

The work by researchers at the Imperial College London is expected to have a positive impact on food safety, improving both health and economic benefits.

Melons, jalapeno and serrano peppers, basil, lettuce, horseradish sprouts and tomatoes are examples of produce that have been linked in recent years to  E coli and Salmonella outbreaks.

The study looked at how these bacterial pathogens latch onto fruits and vegetables. Researchers discovered that strains of Salmonella behave differently when attached to ripe and unripe tomatoes.

“Bacteria (salmonella strains) that attach to ripe tomatoes produce an extensive network of filaments, which is not seen when they attach to the surfaced of an unripe tomato,” Professor Gad Frankel, who heads Imperial’s research team, told the conference. “This could effect how they are maintained on the surface.”

The research team is not sure why bacteria produce filaments on ripe but not unripe fruit. The phenomenon might be due to the surface properties of the tomato or the expression of ripening hormones, Frankel explained. 

The project’s findings are just one example of the subtle interplay between food poisoning microbes and the fresh produce they contaminate and how that determines the way pathogens become established in the food chain, said Frankel.

“Apart from Salmonella, strains of E. coli are also particularly devious in the way they react with plant surfaces, Frankel added.  ”They have hair-like appendages and flagella they can use as hooks to successfully secure themselves onto things like salad leaves.”

The researcher said that “by and large” fresh fruits and vegetables are still safe to eat and provide numerous health benefit.  It just should be recognized that they can transmit harmful bacteria and understanding that can improve food safety.

“Translating research into new policies or methods for decontamination is the challenge for future studies,” said Frankel. 

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