Sequestration of Bacteria and MMPs by Superabsorbent Dressings

Superabsorbent dressings are designed to handle high levels of wound exudate, which may contain harmful microorganisms and excess levels of proteases such as matrix metalloproteinases (MMPs). Managing bacteria, their secretions and host proteases is key in reducing the risk of infection and therefore timely wound healing. We thus evaluated the ability of superabsorbent dressings to sequester bacteria and MMPs.

To assess the ability of dressings to retain bacteria, 6 superabsorbent dressings were inoculated daily, with 107 CFU/ml of Pseudomonas aeruginosa or Staphylococcus aureus for 7 days. Bacteria released from the dressings were visualized by imprints on agar at 1, 3 and 7 days. Furthermore, we quantified bacteria sequestered within the dressing at each time point by disrupting a sample of the inner core and performing standard plate counts. We also assessed sequestration of two key MMPs: MMP-2 and MMP-9. Dressings were saturated and the supernatants collected after 4 days to quantify the release of MMP via ELISA.

There was great variability in the proficiency of dressings to retain bacteria. Visualization of bacteria released onto agar plates showed that only two superabsorbent dressings could retain the bacteria they absorbed. Quantification of bacteria released from the inner core revealed that all dressings retained a significant number of bacteria after 24 hours post-inoculation. However, only 1 dressing maintained a consistent ability to retain bacteria across the day 1, 3 and 7 time points. With respect to sequestration of MMPs, all except one dressing sequestered and retained >98% of MMP-2 and MMP-9.

Our in vitro data showed significant variability in the sequestration of bacteria and MMPs by superabsorbent dressings, suggesting different abilities of these dressings in minimising the risk of infection in highly exuding wounds.

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