Antimicrobial Activity of Silver-Containing Surgical Dressings in an In vitro Direct Inoculation Simulated Wound Fluid Model Against a Range of Gram-Positive and Gram-Negative Bacteria.

Surgical site infections can lead to serious complications and present a huge economic burden. Established wound infections can be difficult to eradicate so preventative measures, including antimicrobial dressings, are advantageous. The antimicrobial activity of an ionic silver, ethylenediaminetetraacetic acid (EDTA) and benzethonium chloride-containing (ISEB) surgical cover dressing (SCD) was compared with two other silver-containing SCDs (silver sulfate and ionic silver carboxymethylcellulose [CMC]) and a non-silver-containing CMC SCD control using an in vitro model. The dressings were tested against a range of gram-positive and gram-negative bacteria found in wound environments, including antibiotic resistant strains, using a direct inoculation simulated wound fluid (SWF) model. Dressings were fully hydrated with SWF and inoculated with a final concentration of 1 × 10 colony forming units (CFU) per 10 microliter of the challenge organisms. Dressings were incubated at 35°C ± 3°C for up to seven days; total viable counts (TVCs) were performed to determine bacterial bioburden. All challenge organism levels remained high for the CMC SCD control and silver sulfate SCD throughout the test period. A greater than 95% reduction in TVCs was observed by four hours for all challenge organisms for the ISEB SCD, with non-detectable levels (<70 CFU per dressing) reached within 24 hours and sustained throughout the test period. Antimicrobial activity was less rapid with ionic silver CMC SCD, with 9 of 11 challenge organisms reaching undetectable levels within 6 to 72 hours. A more rapid antimicrobial activity was observed for the ISEB SCD compared with other dressings tested within this in vitro model.