Professor Bill Keevil, head of the Microbiology Group and director of the Environmental Healthcare Unit at the University of Southampton told FoodProductionDaily.com about the findings of research he co-authored for the November issue of the journal Environmental Microbiology.
The study examined the efficacy of copper used as an antimicrobial biocide against new strains of E.coli, and although it did not examine O104:H4 (the strain apparent in the spring epidemic in Germany and France), the authors found that all the strains investigated died rapidly on copper.
On a dry copper surface, S.L Warnes, V.Caves and C.W Keevil showed that 10m E.coli bacteria were eliminated within 10 minutes, while on a wet copper surface, one could expect a ‘total kill’ within around 45 minutes.
Expensive reputation
Asked about the potential food safety benefits of integrating copper within food processing facilities, Keevil said: “The problem is that people always think of copper as the pure metal. If you’re a French cook, then you know that the best cordon bleu cookery schools use copper pans, they’re expensive.”
He added: “But pure copper isn’t very good in acid conditions. You don’t make jam, for instance, in copper containers, because the fruit acid attacks the copper. But now there is a whole range of alloys, many of which were developed for things such as car motors, other electronic applications.”
Keevil said that such alloys were never investigated to see if they had antimicrobial properties, but that his team had shown that alloys containing more than 60% copper were antimicrobial.
“So there’s a whole family of copper alloys that could be very beneficially in things like food processing. They’re resistant to acid attack, for example, in contact with foods.”
Integrating copper into plants
Asked how copper could be integrated into facilities, Keevil said: “You might be concerned that staff are contaminated. We’ve had Heptatis A, for instance spread via hand contact within food firms, before people eat the contaminated food.
“In that case a copper alloy surface would protect against worker contamination. The other big issue is that the foods themselves are naturally contaminated. O157:H7, for example, is present in contaminated beef, Salmonella and Campylobacter in contaminated chicken.”
Keevil noted that these meats could contaminate, say, salads or tomatoes placed on food contact surfaces after they were removed.
“Protecting against staff, you would certainly be looking at door handles, push plates on doors, etc. But if you’re concerned about contaminated food itself, then the actual food preparation area – cutting areas, conveyer belts, etc. are all very important.”
But with copper trading at around $7,500 on the London Metal Exchange, did Keevil accept that the significant premium involved for food processors using the metal instead of stainless steel?
He said: “When I’ve spoken to metallurgists in the copper industry, they tell me there’s very little difference between the price of stainless steel and copper. All I know is that there isn’t that much of price differential.”
Keevil said he had researched the antimicrobial properties of copper since 1988, and that previous research on contact surfaces within the food industry also showed that copper was also effective against Listeria on both dry and wet copper surfaces.
“We then moved on to the hospital acquired infections, such as MRSA, Clostridium difficile, Acinetobacter baumannii, and again copper was doing a great job,” he added.
Title: ‘Mechanism of copper surface toxicity in Escherichia coli O157:H7 and Salmonella involves immediate membrane depolarization followed by slower rate of DNA destruction which differs from that observed for gram-positive bacteria’
Authors: S.L Warnes, V.Caves and C.W Keevil
Source: Environmental Microbiology, November 2011, doi:10.1111/j.1462-2920.2011.02677.x