| Summary: | 博士 === 國防醫學院 === 醫學科學研究所 === 105 === Part 1
Acinetobacter baumannii is an increasing threat of nosocomial infections in recent years, especially the emergence of multi-drug resistant strains (multi-drug resistant Acinetobacter baumannii; MDRAB). Infections caused by multi-drug resistant A. baumannii could cause longer hospital stay and higher treatment costs. Tigecycline, a board-spectrum tetracycline derivative, is considered as the last antibiotic choice for the MDRAB. However, resistance to Tigecycline was reported following the drug usage worldwide. These resistances are mainly associated with overexpression of efflux pump, especially AdeABC, which is regulated by a corresponding two-component system AdeRS. In the research, we found that the regulatory factor AdeR could recognize the direct repeat on intercistronic region between adeR and adeA. This interaction inhibits the downstream efflux pump expression. In addition, mutations on AdeR DNA binding domain show lower affinity to the direct repeat sequences, and elevate the expression level of efflux pump, leading to high resistance to tigecycline (MIC = 16 μg/mL). This result is very useful for understanding the mechanism of tigecycline resistance of A. baumannii.
Part 2
We generate a silver nanoparticles using green synthesis. In this process, silver nitrate is used as a precursor of silver ions, and then glucose and trimethyl nitrate chitosan (TMCN) are used as a reducing agent and stabilizer, respectively. The whole reaction of silver nanoparticle synthesis could be done at room temperature after adding alkaline solution and mixing thoroughly. There is no need to consume energy or to use expensive equipment. Adjusting the concentration of sodium hydroxide, glucose and TMCN will affect the particle size, zeta potential and formation yield of silver nanoparticles. The average size of this silver nanoparticles (TMCN-AgNPs) is around 60 nm with positive surface charge. The physical and chemical properties of this nanoparticles were characterized by UV-Vis spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The catalytic activity of TMCN-AgNPs was determined by reduction of 4-nitrophenol using NaBH4 as a reducing agent. The antibacterial activity of TMCN-AgNPs was evaluated by broth microdilution method, and was proved to have antibacterial activity against Acinetobacter baumannii, Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus. The minimum inhibitory concentration (MIC) was < 6.13 μg/mL. Moreover, TMCN-AgNPs also showed antibacterial activity against multidrug-resistant Acinetobacter baumannii from clinical isolated, and the MIC value was < 12.25 μg/mL.
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