Antibacterial Mechanism Of Silver Nanoparticles On Multidrug-Resistant Acinetobacter Baumannii

Objective:Infections caused by multidrug-resistant A. baumannii(MDRAB) is increasing which brings great difficulties for clinical treatment. As a new type of nano silver antibacterial agent, the silver nanoparticles(Ag NPs) has extensive and strong antibacterial activity. No drug resistance has been found about Ag NPs, and it shows high safety to mammalian cells. However, the exact antibacterial mechanism of Ag NPs is still not very clear.Previous study showed that Ag NPs can simultaneously induce apoptosis and inhibit new DNA synthesis in the Escherichia coli in a positive concentration-dependent manner. This study presented the first induction of apoptosis and proliferation in the bacteria by Ag NPs in this field. In order to understand the antibacterial activity on multidrug-resistant bacteria and acting mechanism of Ag NPs deeply, we elucidate this mechanism in the view of bacterial apoptosis and proliferation.Methods:A. A total of 38 MDRAB isolated from clinical specimens were classified and analyzed according to endemic areas and specimen types. B. The identification of bacteria and susceptibility test were performed by Vitek 2 Compact bacterial automatic analyzer. C. Multiplex and simplex polymerase chain reaction(PCR) were used to screen for the following resistance genes and insertion sequences. D. Molecular typing of isolates was carried out by enterobacterial repetitive intergenic consensus2-PCR(ERIC2-PCR). E. Colony-Forming Units(CFU) were used to detecting the antibacterial effect of Ag NPs. F. Transmission electron microscope(TEM) was used for the observation of MDRAB morphology treated with Ag NPs. G. Flow cytometry analysis was used to analysis the MDRAB apoptosis. H. Brd U ELISA was used to study MDRAB proliferation.Results: A. The 38 MDRAB were mainly from intensive care unit(ICU). B. In addition to minocycline and tigecycline has not yet appeared resistant strains, the other drug resistance rate of MDRAB were from 47.4% to 100%. C. All of CRAB strains were carrying bla OXA-23 and bla OXA-51 genes and the insertion sequence ISAba1, 2 of which were amplified ISAba125 positive. D. The result of ERIC2-PCR showed that they might derive from the same clone. E. The MDRAB were lagged to growth when exposed with Ag NPs. F. There were several electron dense granules in the centre of MDRAB, but bacterial membrane and wall didn’t have physical damage when co-cultured with Ag NPs. G. Flow cytometry analysis showed that percentage of apoptosis MDRAB is increased, and the increasing trendency is statistical significance. H. The number of newborn MDRAB DNA was found to be significantly decreased when exposed with Ag NPs. Bacterial proliferation was significantly inhibited in the presence of Ag NPs.Conclusions: In this study, we prove that Ag NPs can simultaneously induce MDRAB apoptosis and inhibit new DNA synthesis in a positive concentration-dependent manner. Our findings may provide a new direction for the use of silver nanoparticles in anti-MDR bacteria applications.