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

Abstract

The killing of bacteria on metallic copper surfaces in minutes to hours is referred to as contact killing. Why copper possesses such strong antimicrobial activity has remained enigmatic. Based on the physicochemical properties of metals, it was recently predicted that cadmium should also be active in contact killing [Hans et al., Biointerphases 11, 018902 (2010)]. Here, the authors show that cadmium is indeed antimicrobial. It kills three logs of bacteria in 9 h, compared to copper which kills eight logs of bacteria. Metallic silver kills less than one log of bacteria in 9 h. These findings support the novel concept whereby oxide formation, metal ion dissolution, and a Pearson soft character are the key factors for a metal to be antibacterial. Based on these parameters, copper and cadmium are expected to be the two most antibacterial metals.

Self-disinfecting surfaces and infection control

“…The bactericide mechanism of copper is related to the release of copper ions that cause damage in the bacterial envelop and consequent leakage of the cell content and influx of copper ions into the bacteria. This will generate toxic radicals causing oxidative damage to cellular components and DNA degradation [101].…”

Optimization of Antibacterial Properties of “Hybrid” Metal-Sputtered Superhydrophobic Surfaces

“…These results comply with the physico-chemical properties of each metallic agent. More specifically, silver's bactericidal activity is promoted when found in oxidative condition AgO [51,52], which allows dissolution to Ag + ions that primarily invoke bacterial damage [52,53]. However, oxidation of metallic silver and dissolution to the ionic condition Ag + is pH-dependent, decreasing with increasing pH and being favored in acidic environments [51,54].…”

“…In any case, the release of Cu 2+ ions, which is the main contributor in the killing process [55,56], initiates upon contact with the bacteria [57]. Copper has been proven advantageous in contact killing compared to other metals, including silver [51], and lethal in dry conditions [56,58] that better Bactericidal activity of copper and silver enriched untreated PMMA surfaces (i.e., without plasma micro-nanotexturing) for various Synechococcus sp. PCC 7942 concentrations of (a) 2.3 × 10 9 cfu/mL, (b) 4.6 × 10 9 cfu/mL, and (c) 9.3 × 10 9 cfu/mL.…”

“…On the other hand, copper remains active in ambient conditions, where despite its metallic form, it can be found oxidized as Cu 2 O, which is its main oxidizing state, and CuO, or in the ionic condition Cu 2+ [51]. In any case, the release of Cu 2+ ions, which is the main contributor in the killing process [55,56], initiates upon contact with the bacteria [57].…”

“…In any case, the release of Cu 2+ ions, which is the main contributor in the killing process [55,56], initiates upon contact with the bacteria [57]. Copper has been proven advantageous in contact killing compared to other metals, including silver [51], and lethal in dry conditions [56,58] that better approach our experimental conditions, with a reportedly even higher killing rate in dry copper surfaces compared to moist ones [58]. Its superiority in dry contact can be interpreted by its three-stage attack to bacteria [56], which involves primarily cell membrane rupture and loss of cytoplasmic content due to both released copper ions and applied stress, followed by generation of toxic reactive oxygen species (ROS) by a Fenton-type reaction [59] that damage cell functionality by inhibiting respiration and inactivating proteins, and finally, leading to DNA degradation.…”