Applied Microbiology and Biotechnology

, Volume 91, Issue 1, pp 153–162 | Cite as

The antibacterial activity of biogenic silver and its mode of action

  • Liesje Sintubin
  • Bart De Gusseme
  • Paul Van der Meeren
  • Benny F. G. Pycke
  • Willy Verstraete
  • Nico Boon
Applied Microbial and Cell Physiology


In a previous study, biogenic silver nanoparticles were produced by Lactobacillus fermentum which served as a matrix preventing aggregation. In this study the antibacterial activity of this biogenic silver was compared to ionic silver and chemically produced nanosilver. The minimal inhibitory concentration (MIC) was tested on Gram-positive and Gram-negative bacteria and was comparable for biogenic silver and ionic silver ranging from 12.5 to 50 mg/L. In contrast, chemically produced nanosilver had a much higher MIC of at least 500 mg/L, due to aggregation upon application. The minimal bactericidal concentration (MBC) in drinking water varied from 0.1 to 0.5 mg/L for biogenic silver and ionic silver, but for chemically produced nanosilver concentrations, up to 12.5 mg/L was needed. The presence of salts and organic matter decreased the antimicrobial activity of all types of silver resulting in a higher MBC and a slower inactivation of the bacteria. The mode of action of biogenic silver was mainly attributed to the release of silver ions due to the high concentration of free silver ions measured and the resemblance in performance between biogenic silver and ionic silver. Radical formation by biogenic silver and direct contact were found to contribute little to the antibacterial activity. In conclusion, biogenic nanosilver exhibited equal antimicrobial activity compared to ionic silver and can be a valuable alternative for chemically produced nanosilver.


Biocide Nanoparticles Green chemistry Biological synthesis Drinking water Disinfectant 

Supplementary material

253_2011_3225_MOESM1_ESM.doc (216 kb)
Fig. S1Setups to test direct contact as one of the possible modes of action. a Setup 1 where biogenic silver was added in a dialysis membrane preventing direct contact with E. coli in the surrounding drinking water. b Setup 2 where biogenic silver and E. coli were added together to the Erlemeyer and therefore direct contact was possible; an empty dialysis membrane was present to account for possible sorption of silver ions. Biogenic silver is presented by dashed lines (DOC 216 kb)
253_2011_3225_MOESM2_ESM.doc (412 kb)
Fig. S2Scanning electron microscopy image of biogenic silver. The black dots are silver nanoparticles attached on the cell wall of the bacterial carrier L. fermentum. The bacterium looks black due to closely packed layers of silver nanoparticles covering its surface (DOC 412 kb)


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Copyright information

© Springer-Verlag 2011

Authors and Affiliations

  • Liesje Sintubin
    • 1
  • Bart De Gusseme
    • 1
  • Paul Van der Meeren
    • 2
  • Benny F. G. Pycke
    • 1
  • Willy Verstraete
    • 1
  • Nico Boon
    • 1
  1. 1.Laboratory of Microbial Ecology and Technology (LabMET)Ghent UniversityGentBelgium
  2. 2.Particle and Interfacial Technology GroupGhent UniversityGentBelgium

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