In Vitro Study of Sustained Antimicrobial Activity of a New Silver Alginate Dressing

International Wound Journal

Slone

Linton

et al. 2011

Wound dressings impregnated with silver have a role to play in aiding to reduce both the dressing and wound microbial bioburden. It is therefore imperative that antimicrobial wound dressings have efficacy on a broad range of clinical significant microorganisms. Accordingly, this study aimed to determine the antimicrobial efficacy of a silver alginate dressing against 115 wound isolates that had been isolated routinely from patients at West Virginia University Hospital. Standardised corrected zones of inhibition (CZOIs) were performed on all clinical isolates. It was found that the silver alginate dressing was able to inhibit the growth of all microorganisms tested. In particular, the silver alginate dressing inhibited the growth of Candida albicans and yeasts with CZOI of 3-11·5 mm. All meticillin-resistant Staphylococcus aureus (MRSA) strains were found to be sensitive to the silver alginate dressing with a CZOI range calculated at 3-7·8 mm. Sensitivity to the silver alginate dressing was also evident for S. aureus and vancomycin-resistant Enterococci. CZOIs of 4·25 mm were calculated for Enterococcus faecium and 9·8 mm for viridans streptococcus. The bacteria which demonstrated the highest tolerance to ionic silver included Enterobacter cloacae and Acinetobacter baumannii. Contrary to this the most responsive microorganisms to ionic silver included strains of staphylococci, viridans streptococcus and Candida albicans. No antibiotic-resistant isolates, as identified by Kirby Bauer Clinical Laboratory Standards Institute classification system, were found to be resistant to ionic silver. When a selected number of microorganisms were grown in the biofilm phenotypic state enhanced tolerance to silver was observed, compared to their non biofilm counterparts. Overall, this study has demonstrated the broad antimicrobial activity of a silver alginate dressing on wound isolates grown in the non biofilm and biofilm state. This finding is clinically relevant as both the non biofilm and biofilm phenotypic states of microorganisms are evident in wounds and therefore significant to delayed healing. Consequently, it is imperative that antimicrobial wound dressings demonstrate antimicrobial activity against microorganisms in both phenotypic states.

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

The antimicrobial efficacy of a silver alginate dressing against a broad spectrum of clinically relevant wound isolates

International Wound Journal

Slone

Linton

et al. 2011

“…Silver alginate wound dressings are routinely used in the management of infected wounds, or those wounds considered being at risk of infection as they are known to have antimicrobial activity against a broad range of wound microorganisms, 25 even at different pH values 26 . In a recent in vitro comparative study of a silver alginate and a silver carboxymethyl cellulose dressing, conducted by Bradford et al, 27 it was showed that a silver alginate dressing maintained ionic silver levels at a high enough level that could be sustained for up to 21 days. Unfortunately, sustained antimicrobial efficacy over this time period was not shown for the silver carboxymethyl cellulose dressing on a number of wound isolates.…”

Section: Discussionmentioning

confidence: 99%

Use of flow cytometry to compare the antimicrobial efficacy of silver‐containing wound dressings against planktonic Staphylococcus aureus and Pseudomonas aeruginosa

Wound Repair Regeneration

Slone

Linton

et al. 2011

Self Cite

Silver-impregnated wound dressings continue to be routinely used for the management of infected wounds, or wounds that are at risk of becoming infected. The ability of antimicrobials that have been incorporated into wound dressings to kill microorganisms within the dressing requires appropriate evaluation using in vitro models. In vitro models that have been exploited for this purpose have included the corrected zone of inhibition and the log reduction assay. However, these and other related culturable-based assays are purported to have poor correlation with the overall microbicidal barrier activity of an antimicrobial wound dressing. This is because culturable-based methods only retrospectively indicate bacterial cell death and do not take into account viable but nonculturable states of microorganisms. Consequently, it was the purpose of this study to show that the use of flow cytometry, in conjunction with Syto(®) 9 and propidium iodide, could be used as a method for accurately evaluating and comparing the antimicrobial barrier efficacy of a silver alginate and a silver carboxymethyl cellulose dressing on individual bacterial cells without the need for the use of culturable assays. When a comparison of antimicrobial barrier efficacy on individual planktonic Staphylococcus aureus cells in a simulated wound fluid assay was made between each dressing, enhanced antimicrobial efficacy (as showed by the percentage of dead to alive bacterial cells) of the silver alginate dressing was shown. When Pseudomonas aeruginosa was exposed to both silver-containing dressings, equivalent kill rates were showed for up to 4 days. This result was not significantly different (p<0.05). By utilizing the use of flow cytometric assays, the antimicrobial barrier efficacy of wound dressings can be accurately evaluated enabling differentiation to be achieved between individual dead and live bacteria. The flow cytometric assay is considered a significant advancement to the traditionally used culturable-based methods that are presently used for antimicrobial barrier efficacy testing on planktonic microorganisms.

“…Hence, a loss of antimicrobial efficacy may be anticipated as the silver concentration reduces in the dressing over time, because of the demands of the microbial bioburden. This is important in situations where wound dressings may be in place for several days, with silver alginate dressings recently being shown to demonstrate efficacy for up to 21 days (24). For this reason, to examine the antimicrobial persistence of the test dressing, the CZOI assay was designed to monitor performance over time, up to 13 days, until the antimicrobial effect was no longer apparent.…”

Section: Discussionmentioning

confidence: 99%

“…The use of silver dressings has widely been promoted as a means of reducing the bioburden of wounds without concomitant development of resistant bacterial strains (22) and preventing a wound infection (23). Silver alginate dressings in particular are known to have prolonged antimicrobial efficacy, sometimes as long as 21 days, indicating sustained availability of ionic silver and therefore the requirement of fewer dressings changes (24). Metallic silver is inert, but will release silver ions in an aqueous environment.…”

Section: Introductionmentioning

confidence: 99%

The visualisation and speed of kill of wound isolates on a silver alginate dressing

Hooper

International Wound Journal

Hill

et al. 2012

In chronic wound management, alginate dressings are used to absorb exudate and reduce the microbial burden. Silver alginate offers the added benefit of an additional antimicrobial pressure on contaminating microorganisms. This present study compares the antimicrobial activity of a RESTORE silver alginate dressing with a silver-free control dressing using a combination of in vitro culture and imaging techniques. The wound pathogens examined included Candida albicans, Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, β-haemolytic Streptococcus, and strictly anaerobic bacteria. The antimicrobial efficacy of the dressings was assessed using log(10) reduction and 13-day corrected zone of inhibition (CZOI) time-course assays. Confocal laser scanning microscopy (CLSM) was used to visualise the relative proportions of live/dead microorganisms sequestered into the dressings over 24 hours and estimate the comparative speed of kill. The RESTORE silver alginate dressing showed significantly greater log(10) reductions and CZOIs for all microorganisms compared with the control, indicating the antimicrobial effect of ionic silver. Antimicrobial activity was evident against all test organisms for up to 5 days and, in some cases, up to 12 days following an on-going microbial challenge. Imaging bacteria sequestered in the silver-free dressing showed that each microbial species aggregated in the dressing and remained viable for more than 20 hours. Growth was not observed inside of the dressing, indicating a possible microbiostatic effect of the alginate fibres. In comparison, organisms in the RESTORE silver alginate dressing were seen to lose viability at a considerably greater rate. After 16 hours of contact with the RESTORE silver alginate dressing, >90% of cells of all bacteria and yeast were no longer viable. In conclusion, collectively, the data highlights the rapid speed of kill and antimicrobial suitability of this RESTORE silver alginate dressing on wound isolates and highlights its overwhelming ability to manage a microbial wound bioburden in the management of infected wounds.