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Salad leaves linked to Salmonella growth

20 November 2016

A study undertaken at the University of Leicester has shown that leached juices from leafy vegetables and salad leaves helps to stimulate Salmonella growth and salad leaf colonisation. 

Their research set out to investigate novel methods of preventing food poisoning pathogens from attaching to the surface of salad leaves to help producers improve food safety for consumers.

The study shows that juices from damaged leaves in bagged salad increases Salmonella pathogen growth 2400-fold over a control group. Leached juices also increased the pathogen’s capacity to form a strong and wash-resistant attachment to salad leaves.
 
Even a small amount of damage to salad leaves can massively stimulate the presence of Salmonella in ready-prepared salad leaves. The juices released from damaged leaves also had the effect of enhancing the virulence of the pathogen, potentially increasing its ability to cause infection in the consumer.
 
The research is led by Dr Primrose Freestone of the University’s Department of Infection, Immunity and Inflammation and PhD student Giannis Koukkidis, who has been funded by a Biotechnology and Biological Sciences Research Council (BBSRC) i-case Studentship.
 
Dr Freestone said: “Salad leaves are cut during harvesting and we found that even microliters of the juices (less than 1/200th of a teaspoon) which leach from the cut-ends of the leaves enabled Salmonella to grow in water, even when it was refrigerated. These juices also helped the Salmonella to attach itself to the salad leaves so strongly that vigorous washing could not remove the bacteria, and even enabled the pathogen to attach to the salad bag container.
 
Research published recently by the Food Standards Agency reported that annually there are more than 500,000 cases of food poisoning in the UK. While poultry meat was the most common source of infection, some 48,000 of food poisoning cases were from fresh produce: vegetables, fruit, nuts and sprouting seeds.  Importantly, Salmonella was the pathogen that caused the greatest number of hospital admissions – around 2,500 per year. 


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