JAC Advance Access originally published online on June 18, 2007
Journal of Antimicrobial Chemotherapy 2007 60(2):447-448; doi:10.1093/jac/dkm224
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Correspondence |
The increasing use of silver-based products as antimicrobial agents: a useful development or a cause for concern?—author's response
Antimicrobial Research Centre and Institute for Molecular and Cellular Biology, University of Leeds, Leeds LS2 9JT, UK
Correspondence address. Tel: +44-113-343-5604; Fax: +44-113-343-5638; E-mail: i.chopra{at}leeds.ac.uk
Keywords: silver , toxicity , susceptibility
My recent leading article1 on silver-based products as antimicrobial agents was intended primarily to address microbiological issues such as bacterial susceptibility and the potential for the development of resistance to these products. Consequently, I did not consider the toxicological issues raised by Bayston et al.2 in their comment upon my article.
Obviously, a heavy-metal cation such as silver has the potential to inhibit processes in mammalian cells and as noted by Bayston et al.,2 various forms of silver-associated toxicity have been reported, although fortunately they are rare in clinical practice. Experience with antibiotics tells us that dosing with sub-MIC levels creates conditions favourable for the selection of resistant organisms. Applying these principles to the silver situation led me to conclude that products releasing high levels of silver were unlikely to generate conditions for the selection of silver-resistant microorganisms. However, I agree with Bayston et al.2 that the use of such products could pose a greater risk of toxicity than low silver release formulations and that the therapeutic index for silver-based products may be rather low.
Concerning the issue of zones of inhibition raised by Bayston et al.,2 it may well be true that free silver ions capable of diffusion are not released from nanoparticle systems. Unfortunately, the abstract,3 cited by Bayston et al.,2 does not appear to support this claim. No zones of microbial inhibition were observed with the silver-impregnated catheters used by the authors,3 implying no diffusion of free silver ions from the catheter material. However, there appeared to be insufficient silver in this product even to affect the viability of bacteria (Staphylococcus epidermidis) bound to the catheter surface. Consequently, it is difficult for Bayston et al.2 to argue from these data3 that organisms attached to the surface of the catheter can be killed by silver in the absence of diffusion of the cation from the device.
The author received an educational grant from Smith and Nephew Research to review the literature and prepare the published leading article.1
References
1
Chopra I. The increasing use of silver-based products as antimicrobial agents: a useful development or a cause for concern? J Antimicrob Chemother (2007) 59:587–90.
2 Bayston R, Mills A, Howdle SM, et al. Comment on: The increasing use of silver-based products as antimicrobial agents: a useful development or a cause for concern? J Antimicrob Chemother (2007) doi:10.1093/jac/dkm203.
3 Mills AJ, Ashraf W, Bayston R, et al. Evaluation of the antimicrobial activity of silver-impregnated ventricular catheters. J Hosp Infect (2006) 64:S63–4.
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