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 Study tracks inner workings of the brain with new biosensor
16.08.2018 | Rheinische Friedrich-Wilhelms-Universität Bonn

nachricht Foods of the future
15.08.2018 | Georg-August-Universität Göttingen

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: It’s All in the Mix: Jülich Researchers are Developing Fast-Charging Solid-State Batteries

There are currently great hopes for solid-state batteries. They contain no liquid parts that could leak or catch fire. For this reason, they do not require cooling and are considered to be much safer, more reliable, and longer lasting than traditional lithium-ion batteries. Jülich scientists have now introduced a new concept that allows currents up to ten times greater during charging and discharging than previously described in the literature. The improvement was achieved by a “clever” choice of materials with a focus on consistently good compatibility. All components were made from phosphate compounds, which are well matched both chemically and mechanically.

The low current is considered one of the biggest hurdles in the development of solid-state batteries. It is the reason why the batteries take a relatively long...

Im Focus: Color effects from transparent 3D-printed nanostructures

New design tool automatically creates nanostructure 3D-print templates for user-given colors
Scientists present work at prestigious SIGGRAPH conference

Most of the objects we see are colored by pigments, but using pigments has disadvantages: such colors can fade, industrial pigments are often toxic, and...

Im Focus: Unraveling the nature of 'whistlers' from space in the lab

A new study sheds light on how ultralow frequency radio waves and plasmas interact

Scientists at the University of California, Los Angeles present new research on a curious cosmic phenomenon known as "whistlers" -- very low frequency packets...

Im Focus: New interactive machine learning tool makes car designs more aerodynamic

Scientists develop first tool to use machine learning methods to compute flow around interactively designable 3D objects. Tool will be presented at this year’s prestigious SIGGRAPH conference.

When engineers or designers want to test the aerodynamic properties of the newly designed shape of a car, airplane, or other object, they would normally model...

Im Focus: Robots as 'pump attendants': TU Graz develops robot-controlled rapid charging system for e-vehicles

Researchers from TU Graz and their industry partners have unveiled a world first: the prototype of a robot-controlled, high-speed combined charging system (CCS) for electric vehicles that enables series charging of cars in various parking positions.

Global demand for electric vehicles is forecast to rise sharply: by 2025, the number of new vehicle registrations is expected to reach 25 million per year....

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

LaserForum 2018 deals with 3D production of components

17.08.2018 | Event News

Within reach of the Universe

08.08.2018 | Event News

A journey through the history of microscopy – new exhibition opens at the MDC

27.07.2018 | Event News

 
Latest News

Air pollution leads to cardiovascular diseases

21.08.2018 | Ecology, The Environment and Conservation

Researchers target protein that protects bacteria's DNA 'recipes'

21.08.2018 | Life Sciences

A paper battery powered by bacteria

21.08.2018 | Power and Electrical Engineering

VideoLinks
Science & Research
Overview of more VideoLinks >>>