Variable effects of exposure to ionic silver in wound-associated bacterial pathogens

Silver compounds are used in wound dressings to reduce bioburden. Where infection is not rapidly resolved, bacteria may be exposed to sub-therapeutic concentrations of antimicrobials over prolonged periods of time. In this study, a panel of chronic wound bacteria, Pseudomonas aeruginosa (two strains), Staphylococcus aureus, and Escherichia coli, were exposed to silver nitrate on agar. Phenotypic characterization was achieved using broth microdilution sensitivity testing, a crystal violet biofilm assay, and a wax moth pathogenesis model. Repeated exposure to ionic silver did not result in planktonic phenotypic silver resistance in any of the test panels, although S. aureus demonstrated reversible increases in minimum bactericidal concentration. An ulcer-derived P. aeruginosa exhibited marked reductions in biofilm eradication concentration as well as significantly increased biofilm formation and wax moth killing when compared to the same progenitor. These changes were reversible, trending towards baseline measurements following 10 passages on silver-free media. Changes in virulence and biofilm formation in the other test bacteria were generally limited. In summary, phenotypic adaptation following exposure to ionic silver was manifested other than through changes in planktonic susceptibility. Significant changes in pseudomonas biofilm formation and sensitivity could have implications for wound care regimes and therefore warrant further investigation.

Development and Evaluation of Silver Nanomix as a Next-Generation Tool for Wound Healing and Dressing Applications

This investigation reports silver nanomix as a next-generation, cost-effective, and clinically translatable nanomaterial tool for wound healing and dressing applications. Silver nanomix was developed by systematically hybridizing silver nanoparticles (AgNPs; sub-15 nm; Design Expert tool) with ionic Ag. The silver nanomix elicited significantly higher antibacterial potential than conventional silver products and marketed reference antibiotics, as studied in Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa. Furthermore, the biomechanics of action, safety profile, and intracellular silver organization by silver nanomix are also studied exhaustively. This research presents a viewpoint and direction in designing silver-based antimicrobial dressings with a 40% reduction in their cost.

Protocolo de tratamiento de heridas con apósito de hidrofibra reforzada, con plata iónica al 1,2%, potenciado con EDTA y cloruro de bencetonio para evitar la recurrencia de biopelícula

OBJECTIVE

Present a treatment protocol to avoid biofilm reformation in hard-to-heal wounds, using a hydrofiber dressing with 1.2% ionic silver, ethylenediaminetetraacetic acid and benzethonium chloride.

METHOD

A retrospective, descriptive and analytic study on the use of a treatment protocol, including three case studies. Patient records for hard-to-heal wounds were analysed according to an algorithm for biofilm detection and best-practice recommendations for wound hygiene.

RESULTS

The adopted protocol was based on three pillars: identifying clinical signs suggesting biofilm, performing wound hygiene, and applying an antibiofilm dressing.

CONCLUSION

Wound healing rates can improve after protocol implementation. Adequate control of local signs of infection and exudate, as well as visual and indirect signs of biofilm, were achieved. All patients progressed well towards wound-size reduction and closure using the hydrofiber dressing.

Increased Antibacterial and Antibiofilm Properties of Silver Nanoparticles Using Silver Fluoride as Precursor

Silver nanoparticles were produced with AgF as the starting Ag(I) salt, with pectin as the reductant and protecting agent. While the obtained nanoparticles (pAgNP-F) have the same dimensional and physicochemical properties as those already described by us and obtained from AgNO₃ and pectin (pAgNP-N), the silver nanoparticles from AgF display an increased antibacterial activity against E. coli PHL628 and Staphylococcus epidermidis RP62A (S. epidermidis RP62A), both as planktonic strains and as their biofilms with respect to pAgNP-N. In particular, a comparison of the antimicrobial and antibiofilm action of pAgNP-F has been carried out with pAgNP-N, pAgNP-N and added NaF, pure AgNO₃, pure AgF, AgNO₃ and added NaF and pure NaNO₃ and NaF salts. By also measuring the concentration of the Ag⁺ cation released by pAgNP-F and pAgNP-N, we were able to unravel the separate contributions of each potential antibacterial agent, observing an evident synergy between p-AgNP and the F⁻ anion: the F⁻ anion increases the antibacterial power of the p-AgNP solutions even when F⁻ is just 10 µM, a concentration at which F⁻ alone (i.e., as its Na⁺ salt) is completely ineffective.

Efficacious use of a Calgigraf Ag foam dressing in complete healing of a difficult-to-heal, long-standing ulcer of osteoradionecrosis

A number of dressings containing silver have been recently introduced into the wound care market as increased resistance to antibiotics has become a problem in treating infected wounds. A 54-year-old male, with adenoid cystic carcinoma treated by segmental resection and reconstruction of mandible using reconstruction plate with concomitant radiotherapy, resulted in a deep extraoral nonhealing necrotic, exuding, malodorous, and painful wound. Erythema, eczema, and trophic changes were surrounding the skin. Previous treatment was removal of exposed reconstruction plate and primary closure. Culture samples reported methicillin-resistant Staphylococcus aureus positive and sensitivity to linezolid. Repeated failed attempts to approximate the wound, prompted the use of Calgigraf Ag foam as dressing for the wound. Evidence of new tissue growth and subsequent reduction in wound area and exudate were significant. Chronic nonhealing wounds involving progressive tissue loss give rise to the biggest challenge to wound-care researchers. Despite proper care, some wounds fail to heal in normally and become chronic. The use of ionic silver with negative pressure therapy is safe and effective in difficult nonhealing wounds. This case illustrates the potential benefit of ionic silver combined with negative pressure and moist wound healing as management of a patient with long-standing, nonhealing, and osteoradionecrosis wound. Calgigraf Ag Foam a silver alginate dressing is optimal for maintaining moist environment vital to promote wound healing. It needs less frequent dressing changes with additional benefits such management of excessive exudate minimising malodour and maintaining a moist wound environment.

Sub-cytotoxic concentrations of ionic silver promote the proliferation of human keratinocytes by inducing the production of reactive oxygen species

Silver-containing preparations are widely used in the management of skin wounds, but the effects of silver ions on skin wound healing remain poorly understood. This study investigated the effects of silver ions (Ag⁺) on the proliferation of human skin keratinocytes (HaCaT) and the production of intracellular reactive oxygen species (ROS). After treating HaCaT cells with Ag⁺ and/or the active oxygen scavenger N-acetyl cysteine (NAC), cell proliferation and intracellular ROS generation were assessed using CCK-8 reagent and DCFH-DA fluorescent probe, respectively. In addition, 5-bromo-2-deoxyUridine (BrdU) incorporation assays, cell cycle flow cytometry, and proliferating cell nuclear antigen (PCNA) immunocytochemistry were conducted to further evaluate the effects of sub-cytotoxic Ag⁺ concentrations on HaCaT cells. The proliferation of HaCaT cells was promoted in the presence of 10^-6 and 10^-5 mol/L Ag⁺ at 24, 48, and 72 h. Intracellular ROS generation also significantly increased for 5-60 min after exposure to Ag⁺. The number of BrdU-positive cells and the presence of PCNA in HaCaT cells increased 48 h after the addition of 10^-6 and 10^-5 mol/L Ag⁺, with 10^-5 mol/L Ag⁺ markedly increasing the cell proliferation index. These effects of sub-cytotoxic Ag⁺ concentrations were repressed by 5 mmol/L NAC. Our results suggest that sub-cytotoxic Ag⁺ concentrations promote the proliferation of human keratinocytes and might be associated with a moderate increase in intracellular ROS levels. This study provides important experimental evidence for developing novel silver-based wound agents or dressings with few or no cytotoxicity.

Comparison of in vitro toxicity of silver ions and silver nanoparticles on human hepatoma cells

Scientific information on the potential harmful effects of silver nanoparticles (AgNPs) on human health severely lags behind their exponentially growing applications in consumer products. In assessing the toxic risk of AgNP usage, liver, as a detoxifying organ, is particularly important. The aim of this study was to explore the toxicity mechanisms of nano and ionic forms of silver on human hepatoblastoma (HepG2) cells. The results showed that silver ions and citrate-coated AgNPs reduced cell viability in a dose-dependent manner. The IC50 values of silver ions and citrate-coated AgNPs were 0.5 and 50 mg L(-1) , respectively. The LDH leakage and inhibition of albumin synthesis, along with decreased ALT activity, indicated that treatment with either AgNP or Ag ions resulted in membrane damage and reduced the cell function of human liver cells. Evaluation of oxidative stress markers demonstrating depletion of GSH, increased ROS production, and increased SOD activity, indicated that oxidative stress might contribute to the toxicity effects of nano and ionic forms of silver. The observed toxic effect of AgNP on HepG2 cells was substantially weaker than that caused by ionic silver, while the uptake of nano and ionic forms of silver by HepG2 cells was nearly the same. © 2014 Wiley Periodicals, Inc. Environ Toxicol 31: 679-692, 2016.

Surgical site infections following colorectal cancer surgery: a randomized prospective trial comparing common and advanced antimicrobial dressing containing ionic silver

BACKGROUND

An antimicrobial dressing containing ionic silver was found effective in reducing surgical-site infection in a preliminary study of colorectal cancer elective surgery. We decided to test this finding in a randomized, double-blind trial.

METHODS

Adults undergoing elective colorectal cancer surgery at two university-affiliated hospitals were randomly assigned to have the surgical incision dressed with Aquacel Ag Hydrofiber dressing or a common dressing. To blind the patient and the nursing and medical staff to the nature of the dressing used, scrub nurses covered Aquacel Ag Hydrofiber with a common wound dressing in the experimental arm, whereas a double common dressing was applied to patients of control group. The primary end-point of the study was the occurrence of any surgical-site infection within 30 days of surgery.

RESULTS

A total of 112 patients (58 in the experimental arm and 54 in the control group) qualified for primary end-point analysis. The characteristics of the patient population and their surgical procedures were similar. The overall rate of surgical-site infection was lower in the experimental group (11.1% center 1, 17.5% center 2; overall 15.5%) than in controls (14.3% center 1, 24.2% center 2, overall 20.4%), but the observed difference was not statistically significant (P = 0.451), even with respect to surgical-site infection grade 1 (superficial) versus grades 2 and 3, or grade 1 and 2 versus grade 3.

CONCLUSIONS

This randomized trial did not confirm a statistically significant superiority of Aquacel Ag Hydrofiber dressing in reducing surgical-site infection after elective colorectal cancer surgery.

TRIAL REGISTRATION

Clinicaltrials.gov: NCT00981110.