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 'Living bandages': NUST MISIS scientists develop biocompatible anti-burn nanofibers
16.02.2018 | National University of Science and Technology MISIS

nachricht New process allows tailor-made malaria research
16.02.2018 | Eberhard Karls Universität Tübingen

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: In best circles: First integrated circuit from self-assembled polymer

For the first time, a team of researchers at the Max-Planck Institute (MPI) for Polymer Research in Mainz, Germany, has succeeded in making an integrated circuit (IC) from just a monolayer of a semiconducting polymer via a bottom-up, self-assembly approach.

In the self-assembly process, the semiconducting polymer arranges itself into an ordered monolayer in a transistor. The transistors are binary switches used...

Im Focus: Demonstration of a single molecule piezoelectric effect

Breakthrough provides a new concept of the design of molecular motors, sensors and electricity generators at nanoscale

Researchers from the Institute of Organic Chemistry and Biochemistry of the CAS (IOCB Prague), Institute of Physics of the CAS (IP CAS) and Palacký University...

Im Focus: Hybrid optics bring color imaging using ultrathin metalenses into focus

For photographers and scientists, lenses are lifesavers. They reflect and refract light, making possible the imaging systems that drive discovery through the microscope and preserve history through cameras.

But today's glass-based lenses are bulky and resist miniaturization. Next-generation technologies, such as ultrathin cameras or tiny microscopes, require...

Im Focus: Stem cell divisions in the adult brain seen for the first time

Scientists from the University of Zurich have succeeded for the first time in tracking individual stem cells and their neuronal progeny over months within the intact adult brain. This study sheds light on how new neurons are produced throughout life.

The generation of new nerve cells was once thought to taper off at the end of embryonic development. However, recent research has shown that the adult brain...

Im Focus: Interference as a new method for cooling quantum devices

Theoretical physicists propose to use negative interference to control heat flow in quantum devices. Study published in Physical Review Letters

Quantum computer parts are sensitive and need to be cooled to very low temperatures. Their tiny size makes them particularly susceptible to a temperature...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

2nd International Conference on High Temperature Shape Memory Alloys (HTSMAs)

15.02.2018 | Event News

Aachen DC Grid Summit 2018

13.02.2018 | Event News

How Global Climate Policy Can Learn from the Energy Transition

12.02.2018 | Event News

 
Latest News

Contacting the molecular world through graphene nanoribbons

19.02.2018 | Materials Sciences

When Proteins Shake Hands

19.02.2018 | Materials Sciences

Cells communicate in a dynamic code

19.02.2018 | Life Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>