Copper and brass outperform stainless steel in reducing bacteria

A recent study by Dr. Bill Keevil at the Centre for Applied Microbiology & Research (CAMR) found that E. coli O157:H7 bacteria survive for much shorter periods of time on copper and brass surfaces than on stainless steel.

CAMR, based in Porton Down, UK, is involved in the research, development and production of purified biopharmaceutical products, vaccines and other biologically active compounds.

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 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.

"For centuries, man has used copper and copper alloys to inhibit the growth of harmful microbes," said Dr. Harold Michels of the Copper Development Association in the USA. "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; hmichels@cda.copper.org). Outside the USA: Dr. Chris Lee, ICA (212-251-7241; clee@copper.org)

Edited by Pam AHlberg