The Research Of Antibacterial Activities Of Silver Nanoparticles To Standard Strain And Fluoride-resistant Strain Of Streptococcus Mutans

Objective:To explore the property of two kinds of silver nanoparticles which were prepared by reduction of silver nitrate with glucose and sodium hypophosphite as reducing agents. By detecting the mean diameters of inhibition zone, minimum inhibitory concentrations(MICs) and minimum bactericidal concentrations(MBCs), to investigate the antibacterial effects of two kinds of silver nanoparticles against standard strain and fluoride-resistant strain of Streptococcus mutans.Methods Two kinds of silver colloid nanoparticles were prepared by reduction of silver nitrate with glucose and sodium hypophosphite as reducing agents. The silver nanoparticles were characterized by utilizing ultraviolet-visible absorption spectroscopy (UV-Vis), X-ray diffraction (XRD) and transmission electron microscopy (TEM). Fluoride-resistant strain of Streptococcus mutans was successfully built in our previous experiments. We used the disk diffusion method and broth microdilution method to find the antimicrobial properties of these two silver nanoparticles to standard strain and fluoride-resistant strain of Streptococcus mutans. Dried and sterilized filter paper discs(10mm diameter) were impregnated with the silver colloid nanoparticles solutions using a micropipette. Discs containing the test material were placed on an agar medium uniformly seeded with the test microorganisms. The agar plates were then incubated at37℃for16h to allow microbial growth. The diameters of the zones of inhibition were visualized and measured. The anti-bacterial activity of silver nanoparticles were assessed by determination of their minimum inhibitory concentrations (MICs) against test bacteria. Bacteria were diluted to approximately106organisms/ml in two fold TPY. Silver nanoparticles serial dilutions were made in a concentration range in sterile96-well plastic microdilution trays containing TPY broth. MICs were recorded after incubation for24h at37℃. Minimum bactericidal concentrations were determined by subculturing100ml from each negative well and from the positive growth control onto a nutrient agar plate.Results The silver nanoparticles were spherical with13.40nm and15.50nm mean size and very well dispersed. The mean diameters of inhibition zone of the former nanoparticles to test bacteria were (20.87±0.66) mm、(19.68±0.86) mm respectively, minimum inhibitory concentrations (MICs) were (2.08±0.90)μg/mL、(2.60±0.90) μg/mL and minimum bactericidal concentration(MBCs) were (4.16±1.81) μg/mL,(5.21±1.81) μg/mL.; For the latter nanoparticles, diameters of inhibition zone to test bacteria were (14.86±0.43) mm,(14.19±0.50) mm, MICs were (35.15±12.18) μg/mL、(56.24±24.36)μg/mL, MBCs were(70.30±24.36)μg/mL,(112.48±48.72) μg/mL.Conclusions Glucose and sodium hypophosphite as the reducing agents respectively to reduction aqueous solution of AgNO3can synthesize two kinds of spherical with13.40nm and15.50nm mean size and very well dispersed silver nanoparticles. Both of them exhibited high antibacterial effects against standard strain and fluoride-resistant strain of Streptococcus mutans, the former was better than the latter. While one kind of silver nanoparticles against standard strain and fluoride-resistant strain, the antibacterial property made no difference.