Combined Antibacterial Property and Mechanism of Nanosilver Composites and Antibiotics against Bacteria

The abuse of antibiotics has caused increasingly serious problem of bacterial resistance, thus it is urgent to develop new antibacterial drugs to alleviate this problem. The nanosilver composites that was synthesized from single nanosilver can not only overcome the shortcomings of nanosilver, such as the rapid release rate of Ag+ and unstable physicochemical property, but also reduce the bacterial resistance, which are regarded as a new kind of antibacterial agents with broad application prospects. Previous studies have showed that the combination of single nanosilver and some antibiotics could exhibit the synergistic antibacterial effect. However, little information is available on the performance and mechanism of nanosilver composites combined with antibiotics. In this paper, three kinds of nanosilver composites with different structures were synthesized: silica-polydopamine-nanosilver (SiO2-PD-AgNPs), nanosilver@silica (AgNPs@SiO2) and nanosilver@silica-polydopamine-nanosilver (AgNPs@SiO2-PD-AgNPs). Subsequently, the single toxicity of nanosilver composites to Escherichia coli (E. coli) and Bacillus subtilis (B. subtilis) was determined. The results showed that the toxicity of AgNPs@SiO2-PD-AgNPs to the two kinds of bacteria were greater than that of the other two nanosilver composites. Therefore, AgNPs@SiO2-PD-AgNPs was selected as the representative to determine its combined antibacterial property with KS (kanamycin sulfate)/OH (oxytetracycline hydrochloride), and it was found that the combination of AgNPs@SiO2-PD-AgNPs and KS could display synergistic effect on E. coli/. The nanosilver released by AgNPs@SiO2-PD-AgNPs could react with KS to form the KS-nanosilver complex, resulting in a large amount of Ag+ released from nanosilver. The increase of Ag+ enhanced the permeability of cell membrane, so the amount of Ag+ and KS entering the bacteria were more than that of the antibacterial agents when acting alone, which resulted in greater antibacterial property and a synergistic effect. This study explores the optimal combination and related mechanism of new nanosilver composite and specific antibiotics based on the combined toxicity experiments, which will provide new insight into the development of new antibacterial materials and give a reference for the related combination application of drugs.