Colloidal Silver in action

Colloidal Silver in action

Summary
Silver nanoparticles offer a possible means of fighting antibacterial resistance. Most of their antibacterial properties are attributed to their silver ions. In the present work, we study the actions of positively charged silver nanoparticles against both methicillin-sensitive Staphylococcus aureus and methicillin-resistantStaphylococcus aureus. We use aberration-corrected transmission electron microscopy to examine the bactericidal effects of silver nanoparticles and the ultrastructural changes in bacteria that are induced by silver nanoparticles. The study revealed that our 1 nm average size silver nanoparticles induced thinning and permeabilization of the cell wall, destabilization of the peptidoglycan layer, and subsequent leakage of intracellular content, causing bacterial cell lysis. We hypothesize that positively charged silver nanoparticles bind to the negatively charged polyanionic backbones of teichoic acids and the related cell wall glycopolymers of bacteria as a first target, consequently stressing the structure and permeability of the cell wall. This hypothesis provides a major mechanism to explain the antibacterial effects of silver nanoparticles on Staphylococcus aureus. Future research should focus on defining the related molecular mechanisms and their importance to the antimicrobial activity of silver nanoparticles.

HAADF-STEM micrographs of MRSA cells. (a) MRSA cells surrounded by AgNPs, with AgNPs smaller than 10 nm also being found inside of the cells. (b,c) (1) CWGs. (2) AgNPs interacting with WTAs and CWGs. MRSA cell micrograph shows a cell wall size of 32 nm. The Ag nanoparticle concentration is 23 ppm. (d) (3) Membrane destabilization (≈50 nm).

MRSA STEM images. (a) (1) WTAs and CWGs (≈3 nm). (b) (2) AgNPs interacting with CWGs. (3) Membrane destabilization (≈88 nm). (4) Cytoplasmic leakage. The Ag nanoparticle concentration is 23 ppm.

MSSA cell STEM image. (a) MSSA cell showing AgNP attachment on the cell wall. (b) High magnification STEM images of MSSA cell (1) wall teichoic acids (≈3 nm), (2) interaction of AgNPs with CWGs, (3) destabilization, (4) leakage of cytoplasmic material leading to bacterial cell lysis, (5) cytoplasm, (6) cytoplasmic membrane and (7) cell wall. The AgNP concentration was 11.5 ppm.

SOURCE: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4685924/