Scientists know that Salmonella and E. coli O157, a strain of E. coli that can cause serious sickness in humans, can spread to salads and vegetables if they are fertilized with contaminated manure, irrigated with contaminated water, or if they come into contact with contaminated products during cutting, washing, packing and preparation processes. However, until now, scientists did not understand how the pathogens managed to bind to the leaves.
In new research presented today at the 21st International ICFMH Symposium 'Food Micro 2008' conference in Aberdeen, a new study shows how some Salmonella bacteria use the long stringy appendages they normally use to help them 'swim' and move about to attach themselves to salad leaves and other vegetables, causing contamination and a health risk.
Food poisoning from Salmonella and E. coli is commonly associated with eating contaminated bovine or chicken products, as the pathogens live in the guts of cows and the guts and egg-ducts of chickens, and contamination of meat can occur during the slaughtering process.
However, some recent outbreaks of food poisoning have been associated with contaminated salad or vegetable products, and more specifically, pre-bagged salads. For example, in 2007 a Salmonella outbreak in the UK was traced back to imported basil, and an E. coli outbreak in the USA in 2006 was traced to contaminated pre-packed baby spinach.
In a previous study, Professor Frankel and his colleagues discovered the mechanism by which E. coli 0157 binds to salad leaves. They have shown that E. coli O157 bacteria use short needle-like filaments, which are normally used to inject bacterial proteins into human cells, to attach them to salad leaves, causing contamination and a risk of transmission via the food chain to humans.
Between 1996 – 2000, 23% of the UK's infectious intestinal disease outbreaks like salmonella and E. coli were caused by contaminated food, and of these, 4% were linked to prepared salad.
The new research, led by Professor Gadi Frankel from Imperial College London and carried out with Dr Rob Shaw and colleagues at the University of Birmingham, has uncovered the mechanism used by one particular form of Salmonella called Salmonella enterica serovar Senftenberg, to infect salad leaves, causing a health risk to people who eat them.
Understanding the mechanism that pathogens such as salmonella use to bind themselves to salad leaves is important if scientists are to develop new methods of preventing this kind of contamination and the sickness it causes.
Professor Frankel and his colleagues at the University of Birmingham found that Salmonella enterica serovar Senftenberg bacteria have a secondary use for their flagella - the long stringy 'propellers' they use to move around. The flagella flatten out beneath the bacteria and cling onto salad leaves and vegetables like long thin fingers. To test this observation the scientists genetically engineered salmonella without flagella in the lab and found that they could not attach themselves to the leaves, and the salad remained uncontaminated.
Professor Frankel says: "Discovering that the flagella play a key role in Salmonella's ability to contaminate salad leaves gives us a better understanding then ever before of how this contamination process occurs. Once we understand it, we can begin to work on ways of fighting it."
The team's next steps will involve looking at the extent to which different types of salad leaves are affected by salmonella. Professor Frankel explains that some types of leaves are less susceptible to salmonella contamination that others: "If we can find out what factors affect susceptibility, we may be able to develop new technologies to harness the 'immunity' found in some salad leaves to protect others from contamination," he says.
However, Professor Frankel says that even though such a small minority of cases are currently linked to salads, the numbers are likely to increase in coming years. "In their efforts to eat healthily, people are eating more salad products, choosing to buy organic brands, and preferring the ease of 'pre-washed' bagged salads from supermarkets, then ever before. All of these factors, together with the globalisation of the food market, mean that cases of Salmonella and E. coli poisoning caused by salads are likely to rise in the future. This is why it's important to get a head start with understanding how contamination occurs now," he said.
- PHYSICAL SCIENCES
- EARTH SCIENCES
- LIFE SCIENCES
- SOCIAL SCIENCES
Subscribe to the newsletter
Stay in touch with the scientific world!
Know Science And Want To Write?
- Thinking 'I Can Do Better' Really Can Improve Performance, Study Finds
- Brain Cancer: Why Glioblastoma Is So Difficult To Treat
- Some Celiac Disease May Be Due To Viruses
- Benign Bacteria Block Mosquitoes From Transmitting Zika, Chikungunya Viruses
- Bewildering Dune Formation On Mars
- Little To No Association Between Butter Consumption And Chronic Disease Or Total Mortality
- Can A New Rule Trigger A Second EU Referendum? Petition 4 Millon Signatures, Nearly 12% Of Total Votes Cast
- "Eugenics tends to be a toxic conversation stopper, primarily because of the poisonous political..."
- "Are you proposing pseudo-positive/negative eugenics? As my boss always says, don't point out a..."
- " Media Silent as Concealed Carrier Stops Mass Shooting in Progress at a South Carolina Nightclub..."
- "Thank you for your support - but since the comment you refer to was advocating the shutting down..."
- "Instead of ND, substitute DD, and you have a whole other basket of charlatans - and that comment..."
- The Relationship Between Alcohol and Happiness
- Psst…NRDC Stoners: Your Endocrines Are Disrupted
- College Kids Mostly Blow Off Food-Label Use, Study Finds
- Blue Birds Aren’t Blue, and This is How They Fool You
- ‘Vaxxed’: The Film That No One Saw
- Vice President Joe Biden Threatens the Scientific Community
- Consensus statement: Environmental toxins hurt brain development, action needed
- New anti-cancer strategy mobilizes both innate and adaptive immune response
- Aging population is growing ranks of cancer survivors
- UK government should fund media campaigns that promote quitting, not films that promote smoking
- Report: A host of common chemicals endanger child brain development