Study On The Synergistic Antibacterial Effect Of TeO₂ Combined With Antibiotic Against Multiresistant Staphylococcus Aureus

The wide use of antibiotics is leading to bacteria resistence to antibiotics.The emergence of drug-resistent bacteria,which has become the main pathogenic bacteria in clinic,is contributing antibiotics to bottleneck.Finding a way to effectively reduce bacterial resistance to existing antibiotics is an effective approach to solve the problem of bacterial resistance.It has been reported that nano-silver,nano-zinc oxide and other inorganic nanomaterials in combination with specific antibiotics can effectively reduce the resistance of bacteria to antibiotics.We found that bismuth telluride（Bi₂Te₃）and cefotaxime（CTX）showed the synergistic antibacterial effect against MRSA in our previous study.On this basis,TeO₂nanoparticles were synthesized and the antibiotics which have synergistic anti-MRSA activity when combinated with it were screened to investigate further the synergistic mechanism.The major research works were listed as following:1.Synthesis and characteristics of TeO₂ nanoparticles.TeO₂ was successfully synthesized by a hydrolytic reduction method and characterized by X-ray Diffraction,Atomic Force Microscopy,Dynamic Light Scattering and Fourier Transformed Infrared.The results showed that the as-synthesized TeO₂ nanoparticles were highly purified and spheral–like with 70 nm of diameter.2.Screening the antibiotics which have synergistic anti-MRSA activity with TeO₂.Four classes of antibiotics（β-lactams,aninoglycosides,quinolones and tetracyclines）were chosen to test antibacterial activities with TeO₂ against MRSA by the disk diffusion susceptibility and the chequerboard method.The combination of TeO₂ with CTX showed better synergistic antimicrobial activity against MRSA and the fractional inhibitory concentration index（FICI）was 0.133.3.Study on the synergistic antibacterial mechanism of TeO₂ and CTX against MRSA.The result of quantitative real-time PCR（qRT-PCR）indicated that blaZ gene encodingβ-lactamase expression of MRSA was inhibited after treated by TeO₂combinated with CTX,which meants that the amount ofβ-lactamase in MRSA was decreased.Further,the decreased ofβ-lactamase can reduce the hydrolyzation of the antibiotic,then recovere the antibacterial activity of the antibiotic.The result of qRT-PCR and Western-blot indicated that the transcription and translation level of mecA gene encoding PBP2a were decreased,which partly restore the bond activity of antibiotics to PBP protein.The result of scanning electron microscope（SEM）observation and the determination of membrane potential and reactive oxygen species（ROS）concentration indicated that the combination of TeO₂ with CTX could destroy the membrane structure and induce the higher amount of ROS in vitro,which leading MRSA to death.The cytotoxicity test indicated that the combination presented low cytotoxicity to human normal hepatocyte L02.4.Study on the antibacterial activity of TeO₂ and CTX against the MRSA biofilm.The result of crystal violet staining showed that the combination of TeO₂ with CTX also showed a good inhibitory effect on MRSA biofilm.