New antimicrobial drugs in the pipelineSaturday, May 07, 2011, 16:42 - 16:54
A novel silver colloid: assessment of antibacterial activityR.A. Dixon*, M. Baron (Lincoln, GB)
Objectives: Silver in various forms has been employed in the last few decades for the reduction of pathogen load particularly in Healthcare Associated Infections. The purpose of this study was to determine the preliminary antibacterial effects of a recently developed highly stable novel silver colloid that exhibits exceptional fabrication characteristics and has a narrow particle size distribution. Many previous studies on the effects of silver nanoparticles against microbes have not addressed the importance of the size of the nanoparticles in considering antibacterial effects.
Methods: The antibacterial activities of the silver colloid AC 1 compared to an appropriate silver control were assessed in ‘large volume’ MIC determination both in broth and agar using conventional methodology with a range of inocula . Plastic vessels were used throughout to prevent silver interaction with glass. The activity of AC1 against a MRSA reference strain was tested against a range of concentrations from 16 to 0.2µg/ml incorporated into the agar. The surface was inoculated with appropriate numbers of MRSA. In addition, silver solution was applied to ‘antibiotic’ discs sequentially with drying. Agar plates were inoculated with MRSA and spread. Disks containing silver AC1, and controls were placed on the surface and incubated at either 30 or 37C for 18h
Results: The activity of AC1 against Gram-positive and negative organisms was equivalent. The results were not consistent with previous work in terms of either spectrum or degree of potency. Determinations of AC1 in broth produced only moderate activity against ATCC strains Escherichia coli or Staphylococcus aureus (MIC/MBC = 50/100µg/ml). AC1 in agar test systems produced results remarkably different to those in liquid broth. With lower inocula (105cfu/ml) agar MIC equalled 10µg/ml - at least 5x more active when tested in agar rather than liquid. The number of colonies however exposed to AC1 show significant reduction at concentrations of 5.5µg/ml and partial reduction at 0.6 µg/ml. The activity of AC1 against a single strain of MRSA was confirmed by bioassay producing a significant zone of clearing.
Conclusion: A negatively charged silver phosphate nanoparticle (NP) has been developed by a highly repeatable process that shows interesting activity against a range of pathogen including MRSA.