Antibacterial effect of silver nanoparticles on Staphylococcus aureus.

Antibacterial activity of silver nanoparticles (AgNPs) was investigated using Staphylococcus aureus PTCC1431 as a model of Gram-positive bacteria. The mechanism of antibacterial activity of AgNPs was then studied by analyzing the growth, morphology, and molecular variations in the cell wall. Experimental data showed that AgNPs at a concentration of 4 μg/ml completely inhibited bacterial growth. Transmission electron microscopy results confirmed cell wall damage produced by AgNPs as well as accumulation of AgNPs in the bacterial membrane. Meanwhile, the AgNP-treated bacteria were monitored by circular dichroism to reveal peptidoglycan variations. Some degree of variation in the α-helix position of the peptide chain was observed. Moreover, increasing the AgNP concentration to 8 μg/ml resulted in release of muramic acid (MA) into the medium, which could be attributed to cell wall distraction. A gas chromatography-tandem mass spectrometry analysis and release of MA, as a bacterial indicator, showed that glycan strands may also be decomposed as a result of AgNP treatment.