Study On The Antibacterial Effection And Machenism Of Ag/ZnO Nanocomposite Against Streptococcus Mutans

Dental caries is one of the most common diseases in human oral,which was ranked as the three key combating diseases with cancer and angiocardiopathy by the World Health Organization.Anaerobic Streptococcus mutans(S.mutans)is known as a key inducement of dental caries,which can crosslink with organic material in oral to form dental plaque biofilm.The S.mutans biofilm can not only protect the bacteria cell from external stimulation,but also produce organic acid to corrode the tooth and enhance the antibiotic resistance to bactericide.Hence,it is important to develop novel antibacterial agents with high antibacterial efficiency and low toxicity to combat tooth decay.Zinc oxide(ZnO)has been widely used in clinic as dental materials,however it's antibacterial effect is limited.In this research,Ag/ZnO nanocomposite was synthesized to utilize the antibacterial of Ag nanoparticles itself and the reactive oxygen species(ROS)produced through interaction between Ag and ZnO to enhance the antibacterial ability of the traditional dental materials.Meanwhile,the dental clinical commonly used light-emitting diode(LED)curing light was introduced to enhance the antibacterial activity of Ag/ZnO nanocomposite by amalgamating the photocatalytic and antibacterial properties of Ag/ZnO nanocomposite.The synergistic antibacterial mechanism of Ag/ZnO nanocomposite combined with LED illumination was investigated,which can provide theoretical foundation for the clinical application of Ag/ZnO nanocomposite.The major research works were listed as following:(1)Study on the antibacterial activity and mechanism of Ag/ZnO nanocompositeagainst planktonic S.mutans.The minimal inhibitory concentration(MIC),minimal bactericidal concentration(MBC)and time-kill method were used to test the antibacterial effect of Ag/ZnO nanocomposite against planktonic S.mutans.The result showed that the antibacterial activity of Ag/ZnO nanocomposite against planktonic S.mutans was higher than ZnO.Through the observation of the bacterial morphology by SEM and the measurement of membrane potential,concentration of extracellular K+,ROS and lipid peroxidation level,it illustrated that Ag/ZnO nanocomposite inhibited and killed the planktonic S.mutans by damage the bacterial cell membrane function and oxidizing the large molecules in cells.(2)Study on the antibacterial activity and mechanism of Ag/ZnO nanocomposite against biofilm formation of S.mutans.Crystal violet method was used to test the inhibition of Ag/ZnO nanocomposite on biofilm formation of S.mutans.The result showed that the antibiofilm rate of 128 ?g/m L of Ag/ZnO was over 50%,which was much higher than ZnO.Through measuring the acid production,cell hydrophilic and genes expression such as gtf B,gtf C,com D,come,lux S of S.mutans after exposed to Ag/ZnO,it can illustrated that Ag/ZnO nanocomposite inhibited biofilm formation of S.mutans by prevent its acid production,enhanced its cell hydrophilic and down-regulated biofilm related genes.In addition,the applicatiton of Ag/ZnO in glass ionomer cement was also studed.(3)Study on the synergistic effect and mechanism of Ag/ZnO nanocomposite and LED against S.mutans.LED curing light was introduced in the antibacterial experiment of Ag/ZnO against S.mutans.LED alone has no impact on S.mutans activity.Whenexposed to the combination of LED and Ag/ZnO,the activity of planktonic and biofilm states of S.mutans decreased 2.82 log and 2.40 log respectively compared to exposing to Ag/ZnO alone.The results of SEM and CLSM showed that the morphology of bacteria cell began to change after 3 min,and the amount of death cell in mature biofilm increased from inside to outside when exposed to Ag/ZnO and LED illumination.Electron spin resonance(ESR),intracellular ROS and ROS scavenging tests showed that much of ·OH and·O2-was produced by Ag/ZnO when motivated by LED in a short period of time,which played a key role in antibacterial progress on S.mutans.Moreover,the concentration of ROS increased with the LED illumination time extended.By conjugating Ag/ZnO nanocomposite with LED curing light,the production of exopolysaccharides(EPS)was reduced and the pression of some biofilm related genes were down-regulated,which interpreted the main machenism of S.mutans mature biofilm disruption.