The in-Vitro Antibacterial Activity of Nanocrystalline Silver Dressings Against Bacteria with NDM-1 Carbapenemase

Purpose: Carbapenems are powerful antibiotics, used to treat infections due to otherwise multiresistant bacteria.  The emergence of opportunistic gram-negative bacteria with carbapenem-destroying enzymes, called carbapenemases, is therefore disturbing, since there are few further antibiotics in reserve.  Carbapenemases notoriously include NDM-1, which has repeatedly been imported to the UK via those previously hospitalised in India and Pakistan, where it is widespread.  Bacteria with NDM enzymes can infect many sites, including wounds and are resistant to nearly all antibiotics except colistin, but little is known regarding their resistance to silver compounds. This in-vitro study investigated the antibacterial activity of nanocrystalline silver dressings versus NDM-1 producers. Methods: Five isolates with NDM-1 enzymes (Acinetobacter baumannii, Citrobacter freundii, Enterobacter spp., Escherichia coli and Klebsiella pneumoniae) were tested with three proprietary nanocrystalline silver dressings, and with a non-antimicrobial control.  Dressing samples were inoculated with 0.5 ml of 1x10⁷ cfu/ml inoculum and incubated at 37°C for 0, 0.5, 2 and 4hrs, with reductions calculated vs. T_o control samples. Results: All 3 nanocrystalline silver dressings achieved >4 log₁₀ cfu/ sample reductions in bacterial count within 30 min for all 5 strains.  There was no regrowth up to 4h, and there was no reduction in count by the non-antimicrobial control.   Conclusions: In this study, nanocrystalline silver dressings have been shown to be effective and fast acting in-vitro against bacteria with the NDM-1 enzyme. It is hoped that studies of this type will allow for enhanced clinician education, patient safety and prove beneficial to facilities.