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Antimicrobial Agents and Chemotherapy, December 2007, p. 4453-4461, Vol. 51, No. 12
0066-4804/07/$08.00+0     doi:10.1128/AAC.00605-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Effect of Silver Content on the Structure and Antibacterial Activity of Silver-Doped Phosphate-Based Glasses{triangledown}

Sabeel P. Valappil,1,2 David M. Pickup,3 Donna L. Carroll,4 Chris K. Hope,5 Jonathan Pratten,2 Robert J. Newport,3 Mark E. Smith,4 Michael Wilson,2 and Jonathan C. Knowles1*

Division of Biomaterials and Tissue Engineering,1 Division of Microbial Diseases, University College London, Eastman Dental Institute, 256 Gray's Inn Road, London WC1X 8LD, United Kingdom,2 School of Physical Sciences, University of Kent, Canterbury CT2 7NH, United Kingdom,3 Department of Physics, University of Warwick, Coventry CV4 7AL, United Kingdom,4 School of Dental Sciences, University of Liverpool, Edwards Building, Liverpool L69 3GN, United Kingdom5

Received 8 May 2007/ Returned for modification 27 August 2007/ Accepted 9 September 2007

Staphylococcus aureus can cause a range of diseases, such as osteomyelitis, as well as colonize implanted medical devices. In most instances the organism forms biofilms that not only are resistant to the body's defense mechanisms but also display decreased susceptibilities to antibiotics. In the present study, we have examined the effect of increasing silver contents in phosphate-based glasses to prevent the formation of S. aureus biofilms. Silver was found to be an effective bactericidal agent against S. aureus biofilms, and the rate of silver ion release (0.42 to 1.22 µg·mm–2·h–1) from phosphate-based glass was found to account for the variation in its bactericidal effect. Analysis of biofilms by confocal microscopy indicated that they consisted of an upper layer of viable bacteria together with a layer (~20 µm) of nonviable cells on the glass surface. Our results showed that regardless of the silver contents in these glasses (10, 15, or 20 mol%) the silver exists in its +1 oxidation state, which is known to be a highly effective bactericidal agent compared to that of silver in other oxidation states (+2 or +3). Analysis of the glasses by 31P nuclear magnetic resonance imaging and high-energy X-ray diffraction showed that it is the structural rearrangement of the phosphate network that is responsible for the variation in silver ion release and the associated bactericidal effectiveness. Thus, an understanding of the glass structure is important in interpreting the in vitro data and also has important clinical implications for the potential use of the phosphate-based glasses in orthopedic applications to deliver silver ions to combat S. aureus biofilm infections.

* Corresponding author. Mailing address: Division of Biomaterials and Tissue Engineering, UCL Eastman Dental Institute, 256 Gray's Inn Road, London WC1X 8LD, United Kingdom. Phone: 44 (0)207 915 1189. Fax: 44 (0)207 915 1227. E-mail: j.knowles{at}eastman.ucl.ac.uk

{triangledown} Published ahead of print on 1 October 2007.

Antimicrobial Agents and Chemotherapy, December 2007, p. 4453-4461, Vol. 51, No. 12
0066-4804/07/$08.00+0     doi:10.1128/AAC.00605-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Valappil, S. P., Knowles, J. C., Wilson, M. (2008). Effect of Silver-Doped Phosphate-Based Glasses on Bacterial Biofilm Growth. Appl. Environ. Microbiol. 74: 5228-5230 [Abstract] [Full Text]  


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