Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Bugs dress salad

07.01.2002


Fluorescent labelled E. coli O157:H7 lurk inside lettuce.
© Karl Matthews, Rutgers University


Harmful bugs may lurk within leaves.

Healthy salad greens could be contaminated with bacteria that cause food poisoning, despite thorough rinsing. New research shows that harmful bugs can enter lettuce plants through its roots and end up in the edible leaves1.

Although uncommon, food poisoning caused by eating plants can occur. Vegetables that are fertilized with animal manure, which can contain pathogens, pose the biggest threat. Raw salad vegetables are now washed after harvesting to reduce the risk of contamination.



After an outbreak of poisoning by the potentially fatal O157:H7 strain of Escherichia coli that was connected with prewashed letuce2, food microbiologist Karl Matthews and colleagues at Rutgers University in New Jersey investigated whether bacteria were getting inside the lettuce, rather than just sitting on the leaves. The team grew lettuce in manure inoculated with E. coli O157:H7.

After sterilizing the plants’ surface with bleach, the researchers still found bacteria within the internal tissues that are used for water transport. Lettuce leaves could be infected by simply irrigating plants with bacteria-inoculated water, despite the fact that foliage did not come into direct contact with the water. Small gaps in growing roots are a known port of entry for plant pathogens, and may allow E. coli to get in, the researchers suspect.

Water used to irrigate fields could pose an infection risk, warns Matthews. Although the use of composting manure is regulated, "if you’re using surface irrigation there’s still a chance that the edible portion of the plant can be contaminated", he says.

"No one has checked to see whether [bacteria] are on the surface of the plant or within," agrees William Waites, a food microbiologist at the University of Nottingham, UK. His group’s research reveals a similar uptake of E. coli O157:H7 and Listeria bacteria by spinach. Bacteria also accumulate in the plants over time, the group found. "Levels increased up to 30 days, around the time the plants would be harvested," says Waites.

The concentrations of bacteria used in the lab experiments are probably far higher than those that occur on farms, Matthews points out - after all, poisoning by salad is not common. The team is now working to establish whether salad vegetables grown on farms are also contaminated by E. coli O157:H7 or by other bugs.

"If it is found in saleable plants, it presents us with a new vehicle for E. coli O157:H7," says Tom Cheasty, who directs E. coli O157:H7 surveillance at the UK Public Health Laboratory Service in London. But he adds that, for the moment, there is no compelling reason to treat salad with suspicion.

References

  1. Solomon, E. B., Yaron, S. & Matthews, K. R. Transmission of Escherichia coli O157:H7 from contaminated manure and irrigation water to lettuce plant tissue and its subsequent internalisation. Applied and Environmental Microbiology, 68, 397 - 400, (2002).
  2. Hillborn, E. D. et al. A multistate outbreak of Escherichia coli O157:H7 infections associated with consumption of mesclun lettuce. Archives of Internal Medicine, 159, 1758 - 1764, (1999).


TOM CLARKE | © Nature News Service
Further information:
http://www.nature.com/nsu/020101/020101-10.html

More articles from Health and Medicine:

nachricht Correct connections are crucial
26.06.2017 | Charité - Universitätsmedizin Berlin

nachricht One gene closer to regenerative therapy for muscular disorders
01.06.2017 | Cincinnati Children's Hospital Medical Center

All articles from Health and Medicine >>>

The most recent press releases about innovation >>>

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

Im Focus: Can we see monkeys from space? Emerging technologies to map biodiversity

An international team of scientists has proposed a new multi-disciplinary approach in which an array of new technologies will allow us to map biodiversity and the risks that wildlife is facing at the scale of whole landscapes. The findings are published in Nature Ecology and Evolution. This international research is led by the Kunming Institute of Zoology from China, University of East Anglia, University of Leicester and the Leibniz Institute for Zoo and Wildlife Research.

Using a combination of satellite and ground data, the team proposes that it is now possible to map biodiversity with an accuracy that has not been previously...

Im Focus: Climate satellite: Tracking methane with robust laser technology

Heatwaves in the Arctic, longer periods of vegetation in Europe, severe floods in West Africa – starting in 2021, scientists want to explore the emissions of the greenhouse gas methane with the German-French satellite MERLIN. This is made possible by a new robust laser system of the Fraunhofer Institute for Laser Technology ILT in Aachen, which achieves unprecedented measurement accuracy.

Methane is primarily the result of the decomposition of organic matter. The gas has a 25 times greater warming potential than carbon dioxide, but is not as...

Im Focus: How protons move through a fuel cell

Hydrogen is regarded as the energy source of the future: It is produced with solar power and can be used to generate heat and electricity in fuel cells. Empa researchers have now succeeded in decoding the movement of hydrogen ions in crystals – a key step towards more efficient energy conversion in the hydrogen industry of tomorrow.

As charge carriers, electrons and ions play the leading role in electrochemical energy storage devices and converters such as batteries and fuel cells. Proton...

Im Focus: A unique data centre for cosmological simulations

Scientists from the Excellence Cluster Universe at the Ludwig-Maximilians-Universität Munich have establised "Cosmowebportal", a unique data centre for cosmological simulations located at the Leibniz Supercomputing Centre (LRZ) of the Bavarian Academy of Sciences. The complete results of a series of large hydrodynamical cosmological simulations are available, with data volumes typically exceeding several hundred terabytes. Scientists worldwide can interactively explore these complex simulations via a web interface and directly access the results.

With current telescopes, scientists can observe our Universe’s galaxies and galaxy clusters and their distribution along an invisible cosmic web. From the...

Im Focus: Scientists develop molecular thermometer for contactless measurement using infrared light

Temperature measurements possible even on the smallest scale / Molecular ruby for use in material sciences, biology, and medicine

Chemists at Johannes Gutenberg University Mainz (JGU) in cooperation with researchers of the German Federal Institute for Materials Research and Testing (BAM)...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Plants are networkers

19.06.2017 | Event News

Digital Survival Training for Executives

13.06.2017 | Event News

Global Learning Council Summit 2017

13.06.2017 | Event News

 
Latest News

Study shines light on brain cells that coordinate movement

26.06.2017 | Life Sciences

Smooth propagation of spin waves using gold

26.06.2017 | Physics and Astronomy

Switchable DNA mini-machines store information

26.06.2017 | Information Technology

VideoLinks
B2B-VideoLinks
More VideoLinks >>>