Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Copper Kills Harmful Bacteria, UA Researchers Find

16.07.2012
Copper alloys may make more hygienic cooking surfaces than stainless steel, according to a recent study by Sadhana Ravishankar of the UA department of veterinary science and microbiology. Her lab group discovered that copper alloys have antimicrobial effects against the foodborne pathogen Salmonella enterica.

Each year a tiny, rod-shaped species of bacteria with a fondness for proliferating on human food causes numerous cases of food poisoning around the world, sometimes leading to severe illness and even death.

The culprit, Salmonella enterica, is a leading cause of diarrheal illness worldwide, said Sadhana Ravishankar, an assistant professor in the University of Arizona department of veterinary science and microbiology.
But Ravishankar¹s lab may have discovered a way to reduce the number of food poisoning cases due to Salmonella and possibly other bacteria:

prepare food on surfaces made with materials that contain some amount of the element copper, known as copper alloys.

Ravishankar¹s lab collaborated with Chris Rensing, formerly an associate professor in the UA department of soil, water and environmental sciences and now at Research Triangle Institute International, for the study, which was published recently in the journal Food Microbiology.

³Chris Rensing had already done some research with copper, and he knew that copper surfaces have antimicrobial activity,² said Ravishankar. The International Copper Association donated six samples of copper alloys for the study, including samples of copper mixed with metals such as nickel, iron, chromium, phosphorous and tin that varied in their copper concentration from 60 to 99.9 percent.

Copper is harmful to bacteria because it reacts with oxygen in the atmosphere over time in a process called oxidation, which produces a residue that is toxic to some bacteria. Oxidation is what makes pure copper change in color over time from a rusty gold to a watery green.

³We decided to see the antimicrobial effect of all these copper alloy surfaces on Salmonella,² said Ravishankar. Salmonella was selected as the microbial guinea pig for the study because of its prevalence and the significant harm it causes worldwide because of diarrheal disease.

³Salmonella has caused outbreaks from eating a broad range of different types of foods, including meats and poultry, dairy products, peanut products, ice creams and even chocolate,² said Ravishankar.

She found that because of oxidation, food contact surfaces made of materials containing copper are far less habitable for bacteria than stainless steel, which showed no antimicrobial properties at all.

³Right now, food industries use stainless steel,² said Ravishankar, ³and stainless steel does not seem to have any antimicrobial activity.²

If there are bacteria on a stainless steel surface, she said: ³They will survive for a long time.²

One test by Ravishankar¹s lab manager, Libin Zhu, showed that Salmonella can survive for longer than two weeks on stainless steel surfaces.

By contrast, the bacteria showed significant reductions on copper alloys.
In most cases, Salmonella on steel surfaces dropped in concentration from
10 million cells to 1 million cells, said Zhu. However, on copper alloys, the concentrations of bacteria dropped by a far greater number, to 100 cells or less.

³We tested three copper-resistant strains and one copper-sensitive strain,² said Zhu.

Copper-resistant strains are lineages of bacteria that have been exposed to copper for several generations, long enough for the cells to develop genetic resistance to its antimicrobial effects.

Copper-sensitive strains, by contrast, have never been exposed to copper and are much more susceptible to the toxicity of oxidation.

The researchers placed small samples of each of the Salmonella strains onto the copper alloys, and stored them at different conditions to simulate different types of food processing environments in which the bacteria might exist.

³Salmonella can be a problem in dry foods and wet foods,² Ravishankar said.

Dry foods include products such as peanut butter, almond products and chocolate, while wet foods include vegetables such as tomatoes, lettuce and spinach, milk and other dairy products and anything processed in a wet environment.

Salmonella survived for longer in the simulated wet conditions than in dry conditions, Zhu said.

In addition, ³copper resistant strains under dry conditions only survive for about 15 minutes ­ just about five minutes longer than the sensitive strain.²

In dry conditions, oxidation occurs more quickly because the copper in the surface comes into contact with oxygen in the air.

The researchers further tested how well the bacteria would survive in a nutrient-rich medium versus in a non-nutrient medium.

³The rich medium can protect the cells from the copper,² said Ravishankar.
³We saw survival on the nutrient-rich medium initially, but soon the cells started to die off because of nutrient depletion.²

The researchers also saw that Salmonella cells on alloys with high copper concentrations began to die out much faster than those on surfaces with lower copper concentrations.

For the highest copper concentration Salmonella cells die off in under 30 minutes,² said Zhu. ³But for the other alloys containing lower copper concentrations, the bacteria can survive up to two hours.²

This is still much less than the two weeks survival achieved by Salmonella on stainless steel, leading the researchers to their conclusion: Copper alloys may be more hygienic surfaces for food processing and preparation than stainless steel.

Ravishankar said she would like to do further tests to see if organic materials on a food contact surface, such as crumbs wedged in cracks or leftover protein residues or grease from oils, could change the effectiveness of copper alloys as antimicrobial agents.

³In a food processing environment, there are going to be hard-to-reach areas where you can still have food particles,² said Ravishankar. ³We want to see if the presence of food particles or some kind of organic matter on the copper surfaces changes the efficacy of the copper alloy. Does it become less effective, or is it equally effective?²

Using pure copper is not currently an option, Ravishankar said, due to the high cost of pure copper, and also due to as-yet unresolved concerns that high concentrations of copper residues could potentially have toxic effects on humans as well, if they were ingested.

In the meantime, while using copper alloys as cooking surfaces instead of stainless steel may be slightly more costly, ³it will be worthwhile,² Ravishankar said.

The high antimicrobial potency of copper alloys, she said, has the potential to significantly reduce cases of food poisoning.

Ravishankar¹s study was funded by the International Copper Association, with preliminary research supported by Ravishankar¹s start-up funds from the UA College of Agriculture and Life Sciences.

LINKS:

Research study report: http://www.ncbi.nlm.nih.gov/pubmed/22265316

UA Department of Veterinary Science and Microbiology:
http://microvet.arizona.edu
UA Department of Soil, Water and Environmental Sciences:
http://ag.arizona.edu/swes
CONTACTS:
Researcher Contact:
Sadhana Ravishankar
Department of Veterinary Science and Microbiology The University of Arizona sadhravi@email.arizona.edu

520-621-2355

Media Contact:
Daniel Stolte
University Communications
The University of Arizona
520-954-1964
stolte@email.arizona.edu

Daniel Stolte | University of Arizona
Further information:
http://www.arizona.edu

More articles from Life Sciences:

nachricht How brains surrender to sleep
23.06.2017 | IMP - Forschungsinstitut für Molekulare Pathologie GmbH

nachricht A new technique isolates neuronal activity during memory consolidation
22.06.2017 | Spanish National Research Council (CSIC)

All articles from Life Sciences >>>

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

Quantum thermometer or optical refrigerator?

23.06.2017 | Physics and Astronomy

A 100-year-old physics problem has been solved at EPFL

23.06.2017 | Physics and Astronomy

Equipping form with function

23.06.2017 | Information Technology

VideoLinks
B2B-VideoLinks
More VideoLinks >>>