Potential action of copper surfaces on meticillin-resistant Staphylococcus aureus.

AIMS: Studies to date have shown rapid killing of bacterial cells when exposed to copper surfaces. The mechanistic action of copper on bacterial cells is so far unknown. METHODS AND RESULTS: To investigate potential mechanisms involved, meticillin-resistant Staphylococcus aureus (MRSA) cells (10(7) CFU) were inoculated onto coupons of copper or stainless steel and stained with either the viability fluorophore 5-cyano-2,3-ditolyl tetrazolium (CTC), to detect respiration, or BacLight™ (SYTO9/propidium iodide), to determine cell wall integrity. Coupons were then observed in-situ using epifluorescence microscopy. In addition, DNA from cells inoculated onto either copper or stainless steel surfaces was isolated and analysed by agarose gel electrophoresis. An effect on cellular respiration with CTC reduction was evident but no effect on cell membrane integrity (BacLight™) was observed. Results from the DNA isolation indicated a copper-induced detrimental effect on MRSA genomic material as no bands were observed after exposure to copper surface. CONCLUSIONS: The results indicate that exposure to copper surfaces rapidly kills MRSA by compromising cellular respiration and damaging DNA, with little effect on cell membrane integrity. SIGNIFICANCE AND IMPACT OF THE STUDY: This research provides a mechanistic explanation in support of previous suggestions that although copper surfaces do not affect membrane integrity of cells, there is still a rapid antimicrobial effect.

Effects of temperature and humidity on the efficacy of methicillin-resistant Staphylococcus aureus challenged antimicrobial materials containing silver and copper.

AIMS: To compare silver and copper, metals with known antimicrobial properties, by evaluating the effects of temperature and humidity on efficacy by challenging with methicillin resistant Staphylococcus aureus (MRSA). METHODS AND RESULTS: Using standard methodology described in a globally used Japanese Industrial Standard, JIS Z 2801, a silver ion-containing material exhibited >5 log reduction in MRSA viability after 24 h at >90% relative humidity (RH) at 20 degrees C and 35 degrees C but only a <0.3 log at approximately 22% RH and 20 degrees C and no reduction at approximately 22% RH and 35 degrees C. Copper alloys demonstrated >5 log reductions under all test conditions. CONCLUSIONS: While the high humidity (>90% RH) and high temperature (35 degrees C) utilized in JIS Z 2801 produce measurable efficacy in a silver ion-containing material, it showed no significant response at lower temperature and humidity levels typical of indoor environments. SIGNIFICANCE AND IMPACT OF THE STUDY: The high efficacy levels displayed by the copper alloys, at temperature and humidity levels typical of indoor environments, compared to the low efficacy of the silver ion-containing material under the same conditions, favours the use of copper alloys as antimicrobial materials in indoor environments such as hospitals.

Inactivation of influenza A virus on copper versus stainless steel surfaces.

Influenza A virus particles (2 x 10(6)) were inoculated onto copper or stainless steel and incubated at 22 degrees C at 50 to 60% relative humidity. Infectivity of survivors was determined by utilizing a defined monolayer with fluorescent microscopy analysis. After incubation for 24 h on stainless steel, 500,000 virus particles were still infectious. After incubation for 6 h on copper, only 500 particles were active.

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

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 x 10(7) CFU) mixed with extracted beef juice (25%) was inoculated onto coupons of each copper cast alloy or stainless steel and incubated at either 22 degrees C or 4 degrees 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 degrees C. At 4 degrees 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 degrees C. For stainless steel, no significant reduction in cell numbers occurred. At 4 degrees 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 10(3) CFU resulted in a complete kill for all seven cast copper alloys in 20 min or less at 22 degrees 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.

Potential use of copper surfaces to reduce survival of epidemic meticillin-resistant Staphylococcus aureus in the healthcare environment.

Epidemic meticillin-resistant Staphylococcus aureus (EMRSA) emerged in the early 1980s with EMRSA-15 and -16 being the most prevalent strains within the UK. MRSA transmission between patients is largely via the hands of healthcare workers, and contamination of the hospital environment may occur. The objective of this study was to evaluate the effectiveness of copper and brass to reduce the viability of air-dried deposits of three MRSA strains [MRSA (NCTC 10442), EMRSA-1 (NCTC 11939) and EMRSA-16 (NCTC 13143)] compared with stainless steel. MRSA and EMRSA [10(7)colony-forming units (CFU)] were inoculated on to coupons (1 cm x 1 cm) of copper, brass or stainless steel and incubated at either 22 degrees C or 4 degrees C for various time periods. Viability was determined by resuspending removed CFUs and plating out on tryptone soy agar plates in addition to staining with the respiratory indicator fluorochrome 5-cyano-2,3-ditolyl tetrazolium. On pure copper surfaces, 10(7) MRSA, EMRSA-1 and EMRSA-16 were completely killed after 45, 60 and 90 min, respectively, at 22 degrees C. In contrast, viable organisms for all three strains were detected on stainless steel (grade 304) after 72 h at 22 degrees C. At 4 degrees C, complete kill was achieved on copper for all three strains within 6 h. The results demonstrate an antimicrobial effect of copper on MRSA, EMRSA-1 and -16 in contrast to stainless steel. Consequently, the contemporary application of stainless steel in hospital environments for work surfaces and door furniture is not recommended.