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

Abstract

We have reported previously that copper I and II ionic species, and superoxide but not Fenton reaction generated hydroxyl radicals, are important in the killing mechanism of pathogenic enterococci on copper surfaces. In this new work we determined if the mechanism was the same in non-pathogenic ancestral (K12) and laboratory (DH5α) strains, and a pathogenic strain (O157), of Escherichia coli. The pathogenic strain exhibited prolonged survival on stainless steel surfaces compared with the other E. coli strains but all died within 10 min on copper surfaces using a 'dry' inoculum protocol (with approximately 10(7) cfu cm(-2) ) to mimic dry touch contamination. We observed immediate cytoplasmic membrane depolarization, not seen with enterococci or methicillin resistant Staphylococcus aureus, and loss of outer membrane integrity, inhibition of respiration and in situ generation of reactive oxygen species on copper and copper alloy surfaces that did not occur on stainless steel. Chelation of copper (I) and (II) ionic species still had the most significant impact on bacterial survival but protection by d-mannitol suggests hydroxyl radicals are involved in the killing mechanism. We also observed a much slower rate of DNA destruction on copper surfaces compared with previous results for enterococci. This may be due to protection of the nucleic acid by the periplasm and the extensive cell aggregation that we observed on copper surfaces. Similar results were obtained for Salmonella species but partial quenching by d-mannitol suggests radicals other than hydroxyl may be involved. The results indicate that copper biocidal surfaces are effective for Gram-positive and Gram-negative bacteria but bacterial morphology affects the mechanism of toxicity. These surfaces could not only help to prevent infection spread but also prevent horizontal gene transmission which is responsible for the evolution of virulent toxin producing and antibiotic resistant bacteria.

Lack of Involvement of Fenton Chemistry in Death of Methicillin-Resistant and Methicillin-Sensitive Strains of Staphylococcus aureus and Destruction of Their Genomes on Wet or Dry Copper Alloy Surfaces

“…3B and D). It has been shown that generation of highly toxic hydroxyl radicals via Fenton reaction between Cu(I) and hydrogen peroxide combined with direct copper ion action led to the rapid death of Gram-negative bacteria on copper surfaces (20). The results from this new study suggest that reactive oxygen species (ROS) are involved in bacterial killing on copper but not via Fenton chemistry.…”

The copYAZ Operon Functions in Copper Efflux, Biofilm Formation, Genetic Transformation, and Stress Tolerance in Streptococcus mutans

“…Reports have indicated that, in Gram-positive bacteria, the metal binding sites usually lie within the peptidoglycan layer (88,89). Copper also tends to accumulate on the inner side of the cell membrane, making the inner side more positive and, thus, causing membrane depolarization (11,90). Here, we demonstrated the effect of copper on initiating an immediate membrane potential dissipation, which was significantly higher in the ⌬copYAZ strain than in the wild-type strain.…”

“…In E. coli and Salmonella, contact killing on copper surfaces involves immediate membrane depolarization, leading to compromised cell viability (11). To test whether copper and CopYAZ modulate the membrane potential of S. mutans, we conducted fluorometric assays with bis-oxonol dyes, which can enter depolarized cells and bind intracellular proteins or membranes.…”

“…However, a similar mechanism was not observed in Salmonella enterica serovar Typhimurium, where the addition of exogenous branchedchain amino acids did not revert copper-mediated growth inhibition, thereby suggesting the involvement of a different cellular target for copper toxicity (10). Copper-mediated membrane depolarization has also been reported in E. coli (11). The challenges posed by copper necessitate the involvement of complex regulatory machinery to maintain copper homeostasis in the cell.…”

Disastrous performance of NanoCote/Aqua Based antimicrobial paint in a hospital setting

“…In recent years considerable progress has been made towards elucidating the bactericidal mechanism of copper [21][22][23][24][25][26][27]. There is no need to discuss it here, 1 other than to remark that the release of copper ions from the surface is required, hence the encapsulation matrix should be chosen so as to allow their (slow) release.…”