Chitosan-silver nanoparticles as an approach to control bacterial proliferation, spores and antibiotic-resistant bacteria

Nanoparticulate silver inhibits bacterial growth. Here we evaluated the antimicrobial properties of a novel form of silver nanoparticles, synthesized by a sonochemical method with chitosan as reducing and stabilizing agent (chitosan-silver nanoparticles). The chitosan-silver nanoparticles were positively charged and stable in the long-term, as determined by the high Z-potential. The minimum inhibitory concentration for vegetative bacteria and spores was measured with a resazurin microtiter assay. The interaction between nanoparticles and the bacterial surface was observed by atomic force microscopy and transmission electron microscopy. We found that chitosan-silver nanoparticles inhibited vegetative bacteria and bacterial spores. Furthermore, chitosan-silver nanoparticles enhanced the performance of ampicillin against bacteria and were also effective against an ampicillin-resistant strain. Atomic force microscopy and transmission electron microscopy images revealed a close interaction between the nanoparticles and bacterial extracellular structures, such as flagella. We suggest that chitosan-silver nanoparticles could be used as a topical antimicrobial that can enhance antibiotic performance.