Comparison of the Antimicrobial Activity of Two Post-Operative Hydrocolloid Dressings

Background: Preventing surgical site infection post-surgery is crucial to patient health. In the US, the average rate of surgical site infections (SSIs) is 1.9%. Post-Operative dressings are used on as a barrier to bacterial penetration and to kill bacteria which enter the dressing. Ideally, dressings should demonstrate the ability to achieve >4 log reduction of a wide variety of pathogens that enter the dressing within a number of hours. 

Methods: Antimicrobial testing was performed based on AATCC Test Method 100-2012. Two commercial dressings with hydrocolloid borders were tested, one with a sodium carboxymethylcellulose (CMC) pad containing 1.2% ionic silver#, and the other an alginate plus CMC pad containing 3% ionic silver*. The dressings were challenged with ~1x108 CFU/mL of three relevant bacterial strains, E. Coli (NCIMB 8545), Klebsiella pneumonia (NCTC 10014), and Pseudomonas aeruginosa (ATCC 9027), with log reductions enumerated at 1, 2, 4 and 6 hours post-inoculation.

Results: When compared to a comparable non-antimicrobial control, the 3% ionic silver dressing* reached a >4 log reduction of E. Coli at 4 hours, and a >4 log reduction of Klebsiella pneumonia and Pseudomonas aeruginosa at 2 hours. In comparison, the pure CMC based post-operative dressing with 1.2% silver# only reached a 1.26 log reduction of E. Coli at 6 hours, and required longer to reach the critical r >4 log reduction for the other two organisms, reaching the mark after 4 hours for Pseudomonas aeruginosa, and after 6 hours for Klebsiella pneumonia. 

Conclusion: These results suggest the 3% silver dressing* effectively kills bacteria within the dressing faster compared to the 1.2% silver dressing.  Clinical implications of these in vitro observations are yet to be determined.