Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

How Salmonella bacteria contaminate salad leaves – it’s not rocket science

03.09.2008
How Salmonella bacteria can cause food poisoning by attaching to salad leaves is revealed in new research presented today (3 September) 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.

Danielle Reeves | alfa
Further information:
http://www.imperial.ac.uk

More articles from Life Sciences:

nachricht Nerves control the body’s bacterial community
26.09.2017 | Christian-Albrechts-Universität zu Kiel

nachricht Ageless ears? Elderly barn owls do not become hard of hearing
26.09.2017 | Carl von Ossietzky-Universität Oldenburg

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: The fastest light-driven current source

Controlling electronic current is essential to modern electronics, as data and signals are transferred by streams of electrons which are controlled at high speed. Demands on transmission speeds are also increasing as technology develops. Scientists from the Chair of Laser Physics and the Chair of Applied Physics at Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU) have succeeded in switching on a current with a desired direction in graphene using a single laser pulse within a femtosecond ¬¬ – a femtosecond corresponds to the millionth part of a billionth of a second. This is more than a thousand times faster compared to the most efficient transistors today.

Graphene is up to the job

Im Focus: LaserTAB: More efficient and precise contacts thanks to human-robot collaboration

At the productronica trade fair in Munich this November, the Fraunhofer Institute for Laser Technology ILT will be presenting Laser-Based Tape-Automated Bonding, LaserTAB for short. The experts from Aachen will be demonstrating how new battery cells and power electronics can be micro-welded more efficiently and precisely than ever before thanks to new optics and robot support.

Fraunhofer ILT from Aachen relies on a clever combination of robotics and a laser scanner with new optics as well as process monitoring, which it has developed...

Im Focus: The pyrenoid is a carbon-fixing liquid droplet

Plants and algae use the enzyme Rubisco to fix carbon dioxide, removing it from the atmosphere and converting it into biomass. Algae have figured out a way to increase the efficiency of carbon fixation. They gather most of their Rubisco into a ball-shaped microcompartment called the pyrenoid, which they flood with a high local concentration of carbon dioxide. A team of scientists at Princeton University, the Carnegie Institution for Science, Stanford University and the Max Plank Institute of Biochemistry have unravelled the mysteries of how the pyrenoid is assembled. These insights can help to engineer crops that remove more carbon dioxide from the atmosphere while producing more food.

A warming planet

Im Focus: Highly precise wiring in the Cerebral Cortex

Our brains house extremely complex neuronal circuits, whose detailed structures are still largely unknown. This is especially true for the so-called cerebral cortex of mammals, where among other things vision, thoughts or spatial orientation are being computed. Here the rules by which nerve cells are connected to each other are only partly understood. A team of scientists around Moritz Helmstaedter at the Frankfiurt Max Planck Institute for Brain Research and Helene Schmidt (Humboldt University in Berlin) have now discovered a surprisingly precise nerve cell connectivity pattern in the part of the cerebral cortex that is responsible for orienting the individual animal or human in space.

The researchers report online in Nature (Schmidt et al., 2017. Axonal synapse sorting in medial entorhinal cortex, DOI: 10.1038/nature24005) that synapses in...

Im Focus: Tiny lasers from a gallery of whispers

New technique promises tunable laser devices

Whispering gallery mode (WGM) resonators are used to make tiny micro-lasers, sensors, switches, routers and other devices. These tiny structures rely on a...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

“Lasers in Composites Symposium” in Aachen – from Science to Application

19.09.2017 | Event News

I-ESA 2018 – Call for Papers

12.09.2017 | Event News

EMBO at Basel Life, a new conference on current and emerging life science research

06.09.2017 | Event News

 
Latest News

Nerves control the body’s bacterial community

26.09.2017 | Life Sciences

Four elements make 2-D optical platform

26.09.2017 | Physics and Astronomy

Goodbye, login. Hello, heart scan

26.09.2017 | Information Technology

VideoLinks
B2B-VideoLinks
More VideoLinks >>>