Understanding the antimicrobial activity behind thin- and thick-rolled copper plates

Abstract

The aim of this study was to compare the antibacterial properties of the surfaces of copper plates that were rolled to a thickness of 25 and 100 μm. Differences in topology of 25- and 100-μm-thick copper plates were studied using scanning electron microscopy (SEM), atomic force microscopy (AFM), and X-ray diffraction (XRD). Antibacterial activity of the copper surfaces was tested against strains of Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Listeria monocytogenes, Salmonella typhimurium, Streptococcus sp. BY1, Enterococcus sp. BY2, and Bacillus cereus BY3. Changes in viable cell numbers were determined by plating onto optimal growth media and staining with LIVE/DEAD BacLight™. Changes in metabolic activity were recorded by expression of the luciferase (lux) gene. Cell morphology was studied using SEM. Accumulation and diffusion of copper from cells were recorded using inductively coupled plasma mass spectroscopy (ICP-MS). Lipid and protein oxidation were recorded spectrophotometrically. Surfaces of 25-μm-thick copper plates were rough compared to that of 100-μm-thick copper plates. For most species, a five-log reduction in cell numbers, cell membrane instability, and a decline in metabolic activity were recorded after 15 min of exposure to 25-μm-thick copper plates. Copper accumulated in the cells, and lipids and proteins were oxidized. The rough surface of thinner copper plates (25 μm thick) released more copper and was more antimicrobial compared to thicker (100 μm) copper plates. Cell death was attributed to destabilization of the cell membrane, lipid peroxidation, and protein oxidation.

Copper-Containing Anti-Biofilm Nanofiber Scaffolds as a Wound Dressing Material

“…The outer membrane of Gram-negative bacteria act as barrier to protect the cell from the penetration of biocides and antibiotics [ 41 ]. Accumulation of high levels of copper in the cytoplasm induces a Fenton and Haber-Weiss reaction that mediates lipid peroxidation and cell death [ 8 , 42 ]. The oxidation product of metallic copper, i.e.…”

Killing of bacteria by copper, cadmium, and silver surfaces reveals relevant physicochemical parameters

“…For example, seven logs of wild-type Enterococcus hirae were killed in 12 min in Tris-Cl buffer, in 90 min in growth media, and in 6 h in water; in contrast, only about two logs were killed in 6 h in phosphate buffer. 9,[23][24][25] On the other hand, differences in killing rates due to different bacterial strains are comparatively smaller: >10 7 cfu of five different bacterial biothreat agents were all killed in 0.5-5 min on copper in dry plating experiments. 28 Similarly, >10 7 cfu of five clinical isolates of methicillin-resistant bacteria were killed in 60-270 min, and in another study, >99% of ten clinical isolates were all killed in 2 h in wet plating on copper.…”

“…This variability is mainly due to wet versus dry plating methods and the buffers or media in which the bacteria were applied to copper and, to a minor extent, due to different surface roughness of the coupons and the bacterial strains investigated. 9,[23][24][25] The frequently used phosphate-buffered saline contains a high chloride ion concentration which stabilizes Cu(I), which is considerably more toxic to bacteria than Cu(II). 26 Tris buffer on the other hand strongly complexes Cu(II) and promotes its dissolution.…”

Heavy Metal Resistance Determinants of the Foodborne Pathogen Listeria monocytogenes

“…In relation to iron, recent findings have clarified the role of FrvA, which is implicated in haem toxicity and pathogenicity and is a high-affinity Fe(II)-exporting P-type ATPase with specificity for elemental iron [21,22]. Additionally, a recent study by Yousuf, Ahire, and Dicks elucidated the likely mechanism underlying copper toxicity in L. monocytogenes in which copper disrupts the cell membrane through lipid peroxidation and protein oxidation, as shown in other organisms as well [23,24,25]. Additionally of note from this study was the finding that L. monocytogenes had the most pronounced resistance to copper of all the Gram-positive organisms tested ( L. monocytogenes , Streptococcus spp., Enterococcus spp.…”