Background: Colloidal silver has been used as an antibiotic for at least 100 years. (1) Patients with rheumatoid arthritis may produce antibodies to both Proteus bacteria and to proteins containing citrullinyl residues. Proteus are enterobacteria also found in the upper urinary tract (notably in females),that are able to transform protein-arginyl residues to antigenic protein-citrullinyl residues.
Methods: Anti-arthritic activity was evaluated after orally administering colloidal metallic silver (CMS) to female Wistar rats developing chronic polyarthritis after tailbase injection of either (i) a complete Freund’s adjuvant or (ii) collagen type-II emulsified with an incomplete Freund’s adjuvant or (iii) pristane. Anti-proteus activity was determined by disc diffusion assay by growing P.vulgaris and P.mirabilis on agar plates in the presence of various CMS preparations. Results: A. CMS preparations made electrolytically and administered orally (on alternate days for two weeks) were powerful anti-arthritic agents in rats (ED80 approx. 85 microgm/kg total silver). Monovalent silver preparations (acetate, nitrate, oxide) were ineffective at twice this dose. B. CMS preparations were also more potent than silver salts in suppressing growth of Proteus sp. in vitro. Against P.mirabilis, minimal inhibitory concentrations (MIC) of total silver were greater than 50 nanogm/ml for chemically prepared CMS and less than 6 nanogm/ml for electrolytically prepared CMS: the difference being due to the smaller size of nanoparticles and different Zeta potentials in electrolytic preparations, compared with chemical preparations, of CMS. Conclusions: Pro-arthritic gut micro-organisms may be susceptible to ‘old’ antibiotics taken orally such as colloidal silver, as well as to accepted slow-acting anti-rheumatic drugs (DMARDs) originally developed as antibiotics eg minocycline, dapsone, and salazopyrine. However before CMS can be accepted as a pharmaceutical adjunct, more rigorous Quality Controls must be developed for its preparation and physicochemical characterisation – as well as antimicrobial efficacies and general safety.