I had synthesized silver nanoparticles by reducing silver nitrate using olive and rosemary plant leaves extracts. in The antibacterial test the silver nanoparticles showed more stronger inhibition against gram positive bacteria though in the literature it should be more vigorous against gram negative bacteria. Any one may provide me with plausible reasons.
Thank you so much in advance
Elham
Dear Elham,
The difference in antimicrobial activity between gram positive and gram negative microorganisms is attributed to the structure of their perspective cell walls. The cell wall of gram negative microorganisms is comprised of a thin peptidoglycan layer and a lipopolysaccharide layer. The lipopolysaccharides are composed of covalently linked lipids and polysaccharides with a negative charge, but provide a weak permeability barrier to AgNPs with a positive charge. In contrast, the cell wall of gram positive microorganisms is composed of a thick peptidoglycans layer consisting of linear polysaccharide chains cross-linked by short peptides to form a three dimensional rigid structure. This rigid layer makes it difficult for the AgNPs either to attach to the cell wall or penetrate.
Alham
In case you would need an easy, schematic layout of the Gram-pos./neg. bacterial membrane differences, you may use the pics in my PhD thesis enclosed (p.14-16).
Best regards
Chris