Featured Research

from universities, journals, and other organizations

How Salmonella Bacteria Contaminate Salad Leaves

Date:
September 5, 2008
Source:
Imperial College London
Summary:
How does Salmonella bacteria cause food poisoning by attaching to salad leaves? 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.

Professor Frankel believes that as people eat more salads in an effort to be healthy, cases of Salmonella from salad leaves will increase.
Credit: iStockphoto/Angel Rodriguez

How Salmonella bacteria can cause food poisoning by attaching to salad leaves is revealed in new research presented September 3 at the 21st International ICFMH Symposium 'Food Micro 2008' conference in Aberdeen.

The 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.

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.

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 fertilised 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.

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.

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.


Story Source:

The above story is based on materials provided by Imperial College London. Note: Materials may be edited for content and length.


Cite This Page:

Imperial College London. "How Salmonella Bacteria Contaminate Salad Leaves." ScienceDaily. ScienceDaily, 5 September 2008. <www.sciencedaily.com/releases/2008/09/080902221812.htm>.
Imperial College London. (2008, September 5). How Salmonella Bacteria Contaminate Salad Leaves. ScienceDaily. Retrieved July 30, 2014 from www.sciencedaily.com/releases/2008/09/080902221812.htm
Imperial College London. "How Salmonella Bacteria Contaminate Salad Leaves." ScienceDaily. www.sciencedaily.com/releases/2008/09/080902221812.htm (accessed July 30, 2014).

Share This




More Health & Medicine News

Wednesday, July 30, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Health Insurers' Profits Slide

Health Insurers' Profits Slide

Reuters - Business Video Online (July 30, 2014) Obamacare-related costs were said to be behind the profit plunge at Wellpoint and Humana, but Wellpoint sees the new exchanges boosting its earnings for the full year. Fred Katayama reports. Video provided by Reuters
Powered by NewsLook.com
Concern Grows Over Worsening Ebola Crisis

Concern Grows Over Worsening Ebola Crisis

AFP (July 30, 2014) Pan-African airline ASKY has suspended all flights to and from the capitals of Liberia and Sierra Leone amid the worsening Ebola health crisis, which has so far caused 672 deaths in Guinea, Liberia and Sierra Leone. Duration: 00:43 Video provided by AFP
Powered by NewsLook.com
At Least 20 Chikungunya Cases in New Jersey

At Least 20 Chikungunya Cases in New Jersey

AP (July 30, 2014) At least 20 New Jersey residents have tested positive for chikungunya, a mosquito-borne virus that has spread through the Caribbean. (July 30) Video provided by AP
Powered by NewsLook.com
Generics Eat Into Pfizer's Sales

Generics Eat Into Pfizer's Sales

Reuters - Business Video Online (July 29, 2014) Pfizer, the world's largest drug maker, cut full-year revenue forecasts because generics could cut into sales of its anti-arthritis drug, Celebrex. Fred Katayama reports. Video provided by Reuters
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins