title: Combinatorial activities of ionic silver and sodium hexametaphosphate against microorganisms associated with chronic wounds.
abstract: OBJECTIVE
  There is growing evidence to suggest that biofilms may be involved in the aetiology of chronic wounds. The development of formulations with enhanced anti-biofilm activity could therefore represent a potential therapeutic strategy by reducing bioburdens. Here, the antimicrobial properties of ionic silver and sodium hexametaphosphate (polyphosphate) against bacteria in planktonic form and as biofilms were investigated.
  
  
  METHODS
  The MICs, MBCs and minimum biofilm eradication concentrations (MBECs) of the two test compounds against Candida albicans, Pseudomonas aeruginosa and Staphylococcus aureus were determined. The chequerboard microdilution method was used to determine the fractional inhibitory concentration index (FICI) and fractional biofilm eradication concentration index (FBCI) for the compounds against planktonic bacteria and monospecies biofilms. In addition, biofilms in continuous culture were exposed to hydrogel formulations containing ionic silver and polyphosphate, singly or in combination.
  
  
  RESULTS
  Ionic silver and polyphosphate, when combined, exhibited putative anti-biofilm synergy against P. aeruginosa (FBCI 0.08), C. albicans (FBCI 0.06) and S. aureus (FBCI 0.44). While silver hydrogels reduced the viability of continuous culture biofilms, the incorporation of polyphosphate resulted in significantly greater and more rapid bacterial inactivation (P < 0.05).
  
  
  CONCLUSIONS
  The antimicrobial and anti-biofilm potency of silver hydrogels was markedly enhanced by the incorporation of polyphosphate.
authors.affiliation: School of Pharmacy and Pharmaceutical Sciences, Stopford Building, University of Manchester, Oxford Road, Manchester, M13 9PT, UK.
authors.forename: Gavin
authors.initials: G
authors.lastname: Humphreys
authors.forename: Guat Ling
authors.initials: GL
authors.lastname: Lee
authors.forename: Steven L
authors.initials: SL
authors.lastname: Percival
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: McBain
mesh_terms: D000890:Anti-Infective Agents / Q000494:pharmacology*; D018441:Biofilms / Q000187:drug effects*; D002176:Candida albicans / Q000187:drug effects; D020100:Hydrogels; D008826:Microbial Sensitivity Tests; D010710:Phosphates / Q000494:pharmacology*; D010933:Plankton / Q000187:drug effects; D011550:Pseudomonas aeruginosa / Q000187:drug effects; D012834:Silver / Q000494:pharmacology*; D013211:Staphylococcus aureus / Q000187:drug effects; D014946:Wound Infection / Q000382:microbiology*; D014947:Wounds and Injuries / Q000382:microbiology*
chemical_list: D000890:Anti-Infective Agents; D020100:Hydrogels; D010710:Phosphates; D012834:Silver; C009285:sodium polymetaphosphate