Dual action antimicrobial surfaces via combined nitric oxide and silver release : Dual Action Antimicrobial Surfaces

At the interface between the innate and adaptive immune systems lies the high-output isoform of nitric oxide synthase (NOS2 or iNOS). This remarkable molecular machine requires at least 17 binding reactions to assemble a functional dimer. Sustained catalysis results from the ability of NOS2 to attach calmodulin without dependence on elevated Ca2+. Expression of NOS2 in macrophages is controlled by cytokines and microbial products, primarily by transcriptional induction. NOS2 has been documented in macrophages from human, horse, cow, goat, sheep, rat, mouse, and chicken. Human NOS2 is most readily observed in monocytes or macrophages from patients with infectious or inflammatory diseases. Sustained production of NO endows macrophages with cytostatic or cytotoxic activity against viruses, bacteria, fungi, protozoa, helminths, and tumor cells. The antimicrobial and cytotoxic actions of NO are enhanced by other macrophage products such as acid, glutathione, cysteine, hydrogen peroxide, or superoxide. Although the high-output NO pathway probably evolved to protect the host from infection, suppressive effects on lymphocyte proliferation and damage to other normal host cells confer upon NOS2 the same protective/destructive duality inherent in every other major component of the immune response.

The antibacterial effect and mechanism of action of a silver ion solution that was electrically generated were investigated for Staphylococcus aureus and Escherichia coli by analyzing the growth, morphology, and ultrastructure of the bacterial cells following treatment with the silver ion solution. Bacteria were exposed to the silver ion solution for various lengths of time, and the antibacterial effect of the solution was tested using the conventional plate count method and flow cytometric (FC) analysis. Reductions of more than 5 log(10) CFU/ml of both S. aureus and E. coli bacteria were confirmed after 90 min of treatment with the silver ion solution. Significant reduction of S. aureus and E. coli cells was also observed by FC analysis; however, the reduction rate determined by FC analysis was less than that determined by the conventional plate count method. These differences may be attributed to the presence of bacteria in an active but nonculturable (ABNC) state after treatment with the silver ion solution. Transmission electron microscopy showed considerable changes in the bacterial cell membranes upon silver ion treatment, which might be the cause or consequence of cell death. In conclusion, the results of the present study suggest that silver ions may cause S. aureus and E. coli bacteria to reach an ABNC state and eventually die.