Use of copper cast alloys to control Escherichia coli O157 cross-contamination during food processing

Noyce, J.O., Michels, H. and Keevil, C.W. (2006) Use of copper cast alloys to control Escherichia coli O157 cross-contamination during food processing. Applied and Environmental Microbiology, 72 (6), 4239-4244. (doi:10.1128/AEM.02532-05).

Abstract

The most notable method of infection from Escherichia coli O157 (E. coli O157) is through contaminated food
products, usually ground beef. The objective of this study was to evaluate seven cast copper alloys (61 to 95%
Cu) for their ability to reduce the viability of E. coli O157, mixed with or without ground beef juice, and to
compare these results to those for stainless steel. E. coli O157 (NCTC 12900) (2 107 CFU) mixed with
extracted beef juice (25%) was inoculated onto coupons of each copper cast alloy or stainless steel and
incubated at either 22°C or 4°C for up to 6 h. E. coli O157 viability was determined by plate counts in addition
to staining in situ with the respiratory indicator fluorochrome 5-cyano-2,3-ditolyl tetrazolium. Without beef
extract, three alloys completely killed the inoculum during the 6-h exposure at 22°C. At 4°C, only the
high-copper alloys (>85%) significantly reduced the numbers of O157. With beef juice, only one alloy (95% Cu)
completely killed the inoculum at 22°C. For stainless steel, no significant reduction in cell numbers occurred.
At 4°C, only alloys C83300 (93% Cu) and C87300 (95% Cu) significantly reduced the numbers of E. coli O157,
with 1.5 and 5 log kills, respectively. Reducing the inoculum to 103 CFU resulted in a complete kill for all seven
cast copper alloys in 20 min or less at 22°C. These results clearly demonstrate the antimicrobial properties of
cast copper alloys with regard to E. coli O157, and consequently these alloys have the potential to aid in food
safety.

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Contributors

Author: C.W. Keevil

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