The WOCN Society 40th Annual Conference (June 21-25th, 2008)


2405

Antimicrobial Activity of Antimicrobial Silver Containing Hydrocellular Foam Dressings in Comparison to Various Silver-based Antimicrobial Dressings against MRSA Via a Dynamic Shake Flask Method

David W. Brett, BS, BS, MS, Smith & Nephew, Science & Technology Manager, 11775 Starkey Rd, Largo, FL 33773

In this study, log reduction was used to compare the antimicrobial activity of antimicrobial hydrocellular foam dressings containing silver to other silver-based dressings against Methicillin Resistant Staphylococcus aureus (MRSA). This in vitro method employs a 5ml suspension of organism to challenge an antimicrobial dressing over a specified time period. Samples are inoculated with a clinically relevant quantity of organisms and subsequently numbers of surviving bacteria remaining are assessed over time. The dynamic nature of the test ensures good contact with the bacteria and the antimicrobial foam, whilst being emulative of movements in dressing wear. The result is quoted as a log reduction the sample has achieved, at each time point, compared with a control count at the start of the test.  Testing was carried out on 2 cm x 2 cm pieces of each dressing using a 5ml dynamic shake flask test method (replicates of six).  Dressings were challenged against 5ml of culture inoculum containing approximately 1x105 cfu/ml using a 60ml vessel. Samples were incubated under dynamic conditions at 32oC for 0, 0.5, 2, 4 and 24 h. Following incubation at each sample time point, the dressings were removed and 3ml of the resulting suspension neutralized to arrest antimicrobial activity. The number of surviving micro-organisms was enumerated using standard pour plate techniques and the log reduction for the antimicrobial dressings calculated by subtracting the mean value obtained for the non-antimicrobial control.  Dressings A, B and C generated  log10 reductions of >3.0 at 24 hrs. However, dressings D, E, F, and G failed to generate over a 3 log10 reduction at 24 hrs. In antimicrobial activity testing, silver is considered bactericidal if it achieves log10 reductions of 3 log10 or greater. In this study, only dressings A, B and C were able to generate bactericidal activity against MRSA at 24 hrs.


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