Antibacterial Properties of Copper and Brass Demonstrate Potential to Combat Toxic E.coli O157 Outbreaks in the Food Processing Industry

September 6, 2000


NEW YORK- A recent study by Dr. Bill Keevil at the Centre for Applied Microbiology & Research (CAMR) found that the highly toxic E. coli O157:H7 strain of bacteria survive for much shorter periods of time on copper and brass surfaces than on stainless steel. This finding has wide-ranging implications for reducing outbreaks from cross contamination of E. coli O157 in the food processing industry.

The work carried out by CAMR team member Dr. Andrew Maule found that at room temperatures it takes 34 days for E. coli O157 bacteria to die on stainless steel tiles, 4 days to die on brass tiles, and just 4 hours to die on copper tiles. At chill temperatures typical of food storage, the study found that ten percent of the bacteria were still alive on stainless steel tiles after 34 days, whereas bacteria were completely eradicated on brass tiles within 12 days and on copper tiles in just 14 hours.

These results prompted the International Copper Association to commission CAMR, Porton Down, U.K., to further investigate the bactericidal properties of copper, brass, and stainless steel surfaces in various conditions found in the food preparation industry. It was found, for example, that in acidic environments representative of fruit juice processing, E. coli O157 survived for as little as 45 minutes on copper, versus 2 days on stainless steel. And in environments containing animal feces with anaerobic E. coli O157 bacteria, copper and brass tiles were found to exhibit superior bactericidal effects to stainless steel tiles.

"It may be possible to achieve important public health benefits just by changing the surface material commonly used in food processing," said Dr. Keevil. "Stainless steel is the most widely used surface in food preparation, but this material can remain a repository of microbial food contamination for a very long period of time." Since copper-bearing materials have such strong antibacterial properties, the researchers believe that foods most amenable for processing on copper surfaces should be determined in order to reduce E. coli O157 occurrences and outbreaks.

"We now have a preliminary understanding of the bactericidal benefits of copper and brass over stainless steel in combating cross contamination from E. coli O157," said Keevil. "Our findings point to the potential use of copper and other copper alloys, such as copper-nickel, nickel silver and brass, as hygienically beneficial surfaces in the food processing industry." Plans are under consideration to investigate the antibacterial effect of copper and selected alloys on Salmonella enteritidis PT4, S. typhimurium DT104, Campylobacter jejuni, and other highly toxic bacteria.

Dr. Harold T. Michels of the Copper Development Association in the USA hailed the study as a significant stride in putting copper to work combating human health problems. "For centuries, man has used copper and copper alloys to inhibit the growth of harmful microbes," said Michels. "We look forward to practical applications that may spring from this study which would control harmful bacteria, particularly related to food hygiene."

ICA currently seeks partners to conduct further investigations on the potential of copper alloys to reduce the occurrence of E. coli O157 cross contamination in the food industry. Interested parties in food processing, food appliances, and related industries are encouraged to contact:

In the USA: Dr. Harold Michels, CDA
(212-251-7224; Email)

About ICA:

The above study was funded by the International Copper Association (ICA). ICA is responsible for communicating the benefits of copper and promoting worldwide copper initiatives in the power, information, plumbing, and architectural markets, as well as in other applications. ICA operates in 29 locations worldwide. Its members represent 80% of the world's refined copper output. Its associate members are among the largest fabricators of copper and copper alloys in the world. For further information, contact: International Copper Association, Ltd., 260 Madison Avenue, New York, NY 10016-2401. Tel: (212) 251-7240. Fax: (212) 251-7245.

About Escherichia coli (E. coli) O157:H7

E. coli O157:H7 is a highly infectious, ACDP Hazard Group 3 foodborne and waterborne pathogen that has created a serious public health challenge for the food processing industry. This strain of bacteria produces potent verocytotoxins, which can cause hemolytic colitis, hemolytic uremic syndrome (kidney disease), and even death.

E. coli O157 bacteria infect tens of thousands of people around the world every year. An outbreak in Japan caused 9,000 people to become sick. A 1997 outbreak in Scotland was responsible for 500 infections and 20 deaths. And in the USA., over 500 people became ill and three children died after eating undercooked hamburgers infected with E. coli O157.

It is believed that just ten to fifty highly toxic E. coli O157 organisms are sufficient to infect humans with illness. The infections are difficult to treat and antibiotics may prompt the bacteria to release even more verocytotoxins. In healthy individuals, E. coli O157 infections usually last three to five days. However, this bacterium can victimize children under 14 years of age, the elderly, and immunocompromised individuals with serious complications.

  1. Background on E. coli O157

    What is E. coli O157?
    E. coli O157 is a highly infectious ACDP Category 3 foodborne and waterborne pathogen that has become a serious public health problem in the past three decades. E. coli O157 bacteria produce potent toxins which cause diarrhea, severe aches, and nausea in infected persons, and the bacteria may cause hemolytic colitis (bloody diarrhea), kidney disease (hemolytic uremic syndrome), and even death. Children up to 14 years of age, the elderly, and immunocompromised individuals are at the greatest risk of contracting severe symptoms.

    How prevalent are E. coli O157 infections?
    Very prevalent. It is estimated that hundreds of thousands of people become ill and hundreds of people die each year due to E. coli O157 infections.

    How does E. coli O157 infect the population?
    Contaminated meat, water, dairy products, and non-pasteurized juices are the most common pathways for contracting E. coli O157 bacteria. Direct contact with an infected person is also a means for infection.

    How does E. coli O157 infect food supplies?
    Fecal contamination from the intestines of cattle and sheep during slaughter is one of the most prevalent pathways for infection. In 1993, 500 people became ill and three children died in the State of Washington after eating undercooked hamburgers infected with E. coli O157. Similar outbreaks have been reported in Japan and the United Kingdom.

    What is cross contamination?
    A carcass that is infected with E. coli from its own intestines is said to be "contaminated." However, a carcass that is not infected with E. coli from its own intestines may accidentally contact a contaminated carcass or come in contact with a contaminated surface. When this happens, the carcass becomes "cross contaminated."

  2. The Protective Properties of Copper and Brass Surfaces in Food Preparation

    What is the potential role of food preparation surfaces in reducing the risk of E. coli O157 infections?
    Researchers have found that some food preparation surfaces, such as copper and brass, have a bactericidal effect on E. coli O157 bacteria. Since infected carcasses in food preparation can contaminate work surfaces, the risk of cross contamination of non-infected carcasses can be reduced by using a surface that exhibits a bactericidal effect on the microbes. Copper and brass surfaces may reduce the potential for cross- contamination of food by pathogenic organisms, such as E. coli O157, and hence play a hygienic role in the food processing industry.

    What is the most prevalent surface material in the food preparation industry?
    Stainless steel is the most widely used surface material in food processing. It is nontoxic and easy to clean. However, stainless steel scratches, harbors microbes if not disinfected frequently, and does not exhibit the bactericidal properties of copper and brass.

    What are the potential advantages of copper and brass to stainless steel?
    CAMR researchers found that bacteria can live on stainless steel surfaces for a very long time (e.g., several months). This means that the surface itself can become a source of cross contamination. Other CAMR workers have shown that carcasses that were not directly contaminated with E. coli O157-infected feces, for example, can become cross contaminated by contacting infected stainless steel surfaces.

    CAMR researchers also found that E. coli O157 dies off much more quickly on copper and brass surfaces than on stainless steel surfaces. Their preliminary study suggested that copper and brass are much more hygienic as a food preparation surface than stainless steel.

    Furthermore, copper and brass are much less expensive than stainless steel.

    How much better are copper-bearing surfaces than stainless steel as bactericides?
    Much better. At room temperature (20 0C), all of the E. coli O157 bacteria died on copper tiles within just 4 hours. Alternatively, it took 34 days for all of the bacteria to die on the stainless steel tiles. Survival rates on brass were 4 days.

    At chill temperatures typical of food storage (4°C), all of the E. coli O157 bacteria died on the copper tiles within 14 hours. Alternatively, after 34 days, 10% of the bacteria were still alive on the stainless steel tiles. Survival rates on brass were 12 days.

    What variables in food processing conditions were studied in the research?
    The antimicrobial effects of brass were dramatically accelerated with anaerobically-grown microbes (i.e., microbes that thrive in the absence of oxygen, such as in the gut of animals). The antimicrobial effects of copper were delayed slightly for anaerobically-grown microbes.

    Low pH conditions typical in the manufacturing of fruit juice increased the mortality rate of E. coli O157 on copper surfaces to just 45 minutes. The microbes died in two days on stainless steel surfaces.

    When human and animal feces containing the anaerobic form of the bacteria were studied, the antimicrobial effects of copper and brass remained significant. On stainless steel, the mortality rates of the bacteria decreased, but to a still unacceptable level of several weeks.

    Highly humid conditions were found to reduce the antimicrobial effect of copper-bearing surfaces.

    Mortality of the microbes in UHT milk (representative of dairy environments) were reduced to 24 hours on brass, but increased slightly on copper.

    Where do we go from here?
    Copper and brass have the potential to become more hygienic surface materials than stainless steel in the food processing industry. Therefore, it is worthwhile to study the bactericidal effects of these three surfaces on other highly toxic bacteria, such as Salmonella enteritidis PT4, Campylobacter jejuni (poultry); and the multiple antibiotic resistant
    S. typhimurium DT104 (beef).

    Furthermore, it is worthwhile to: 1) investigate any potential leaching characteristics of copper-bearing food preparation surfaces, 2) explore copper alloys for use in food preparation when a material required must be harder than copper, and 3) study the potential toxicological effects of leached copper in various types of processed foods.