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 Scientists unlock ability to generate new sensory hair cells
22.02.2017 | Brigham and Women's Hospital

nachricht New insights into the information processing of motor neurons
22.02.2017 | Max Planck Florida Institute for Neuroscience

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Breakthrough with a chain of gold atoms

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

Im Focus: DNA repair: a new letter in the cell alphabet

Results reveal how discoveries may be hidden in scientific “blind spots”

Cells need to repair damaged DNA in our genes to prevent the development of cancer and other diseases. Our cells therefore activate and send “repair-proteins”...

Im Focus: Dresdner scientists print tomorrow’s world

The Fraunhofer IWS Dresden and Technische Universität Dresden inaugurated their jointly operated Center for Additive Manufacturing Dresden (AMCD) with a festive ceremony on February 7, 2017. Scientists from various disciplines perform research on materials, additive manufacturing processes and innovative technologies, which build up components in a layer by layer process. This technology opens up new horizons for component design and combinations of functions. For example during fabrication, electrical conductors and sensors are already able to be additively manufactured into components. They provide information about stress conditions of a product during operation.

The 3D-printing technology, or additive manufacturing as it is often called, has long made the step out of scientific research laboratories into industrial...

Im Focus: Mimicking nature's cellular architectures via 3-D printing

Research offers new level of control over the structure of 3-D printed materials

Nature does amazing things with limited design materials. Grass, for example, can support its own weight, resist strong wind loads, and recover after being...

Im Focus: Three Magnetic States for Each Hole

Nanometer-scale magnetic perforated grids could create new possibilities for computing. Together with international colleagues, scientists from the Helmholtz Zentrum Dresden-Rossendorf (HZDR) have shown how a cobalt grid can be reliably programmed at room temperature. In addition they discovered that for every hole ("antidot") three magnetic states can be configured. The results have been published in the journal "Scientific Reports".

Physicist Dr. Rantej Bali from the HZDR, together with scientists from Singapore and Australia, designed a special grid structure in a thin layer of cobalt in...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Booth and panel discussion – The Lindau Nobel Laureate Meetings at the AAAS 2017 Annual Meeting

13.02.2017 | Event News

Complex Loading versus Hidden Reserves

10.02.2017 | Event News

International Conference on Crystal Growth in Freiburg

09.02.2017 | Event News

 
Latest News

Microhotplates for a smart gas sensor

22.02.2017 | Power and Electrical Engineering

Scientists unlock ability to generate new sensory hair cells

22.02.2017 | Life Sciences

Prediction: More gas-giants will be found orbiting Sun-like stars

22.02.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>