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Proceedings of the 31 st European Peptide SymposiumMichal Lebl, Morten Meldal, Knud J. Jensen, Thomas Hoeg-Jensen (Editors)European Peptide Society, 2010Silver Nanoparticle Influence on Staphylococcus aureusPeptidoglycan Cell WallFateme Mirzajani * , Alireza Ghassempour, Atousa Aliahmad, andMohammad Ali EsmaeiliMedicinal Plants and Drugs Research Institute, Shahid Beheshti University, G.C.Evin, Tehran, IranIntroductionColloidal silver nanoparticles (AgNPs) with sizes smaller than 100 nm in at least onedimension, have recently received a lot of attention and concern due to their anti-microbialactivity [1]. It is obvious that silver, whether in the ionic or nanoparticle form, hasinteractions with the bacterial cell wall [2]. The peptidoglycan (PGN) is a specific andessential structural element in the cell wall of almost all bacteria. Its main structuralfeatures are linear glycan strands cross-linked by short peptides. The glycan strands aremade up of alternating N-acetylglucosamine and N-acetylmuramic acid (MA) residueslinked by -1 4 bonds [3], and the peptide is composed of L-alanine, D-glutamine,L-lysine, and D-alanine in the case of Staphylococcus aureus.Results and DiscussionAs can be seen from the UV spectra in Figure 1a, the max of colloidal AgNPs was 426 nm.The DLS analysis (Figure 1b) of synthesized AgNPs demonstrates that their size, volumemean diameter (VMD), and surface mean diameter (SMD) were 18.34 nm (X 99 ), 4.10 nm,and 2.26 nm, respectively. Anti-Staphylococcal properties of AGNPs were confirmed bythe macro-broth dilution susceptibility tests (MIC = 2 µg/ml and MBC = 4 µg/ml).To evaluate the influenceof AgNPs on the bacterialPGN cell wall and specificallyits peptide part, their CDspectra were recorded inDMSO. Figure 2a demonstratesthe CD spectra in theFig. 1. (a) UV absorbance spectra, (b) DSL, (c) TEMimage of Ag colloids.peptide-bond absorptionregion (200–260 nm) ofirradiated PGNs. In the regionof 210-220 nm, a noticeablechange can be observed. Inview of the fact that thisregion involves the characteristicwavelengths of the hydrogen bond and α-helix as well as the peptide secondarystructure, it can be concluded that AgNPs mostly affected the peptide hydrogen bonds.The electron density images of the treated S. aureus are illustrated in Figure 2b and 2c.The dark and light areas show where the sample had a high and low electron density,respectively. Theimages of the samplestreated with AgNPswere greatly differentfrom those of theuntreated cells (Figure2b). The PGNs'fragmentation aftertreatment (Figure 2c)proves their interactionwith AgNPs,which caused the cellwall destruction in S.aureus.Fig. 2. (a) CD spectra of PGN (.-), PGN treated with AGNPafter 30 min. (..) and 3 h. (-). Transmission electron microscopyimages of S. aureus before (b) and after 24 h (c) AGNPtreatment.274