沙门菌是重要的人兽共患病病原，也是引起全球食源性疾病暴发的首要病原菌。目前沙门菌多重耐药现象日益严重。外排泵被认为是大肠杆菌和沙门菌多重耐药性的最重要的机制，其激活后能够将进入细胞内的药物进行非选择性的主动外排，导致细菌产生多重耐药性。AcrAB-TolC是革兰氏阴性菌中最主要也是研究得最为透彻的外排泵，其激活（表达）受局部和整体调控蛋白相互之间复杂、缜密的调控，其中RamA, MarA和SoxRS对AcrAB-TolC表达的调控作用尤其重要，它们可以独立或交互作用来调控AcrAB-TolC的表达。目前RamA与MarA和SoxRS之间如何协同调控AcrAB-TolC表达的机理还不明了。本项目拟针对养殖场分离和实验室诱导的耐药沙门菌，通过基因敲除的方法，构建目的基因缺失菌株，采用RT-PCR方法，探讨 RamA与MarA和SoxRS协同调控AcrAB-TolC表达的机制。

Salmonella spp. are common zoonotic pathogen, and non-typhoidal Salmonella (NTS) are one of the most common causes of food and water borne infections, and the emergence and transmission of multi-drug resistant (MDR) strains that may pass from food animals to humans is a public health concern. The multi-drug resistant Salmonella from food animal in China is increasing, with high level of resistance to a broad spectrum of drug surpassing greatly that in developed countries. The multiple antibiotic resistance (mar) locus of E. coli and Salmonella is recognized as the most important intrinsic system, which mediate resistance primarily by up-regulating efflux of some antibiotics, disinfectants and organic solvents via the AcrAB-TolC efflux pump and down regulating influx through Outer Membrane Protein. Whilst the level of antibiotic resistance conferred by AcrAB-TolC is only moderate, but possibly as a 'stepping stone' to higher levels of resistance through MarA and RamA and SoxS. It is still unclear on the regulation between RamA and MarA, and RamA and SoxS on the expression of AcrAB-TolC. In this proposal, we focus on multi-drug resistant Salmonella spp. obtained from food animal, and step-wise selected with sub-inhibitory concentration or increasing concentration of ciprofloxacin,investigate the expression of RamA, MarA, and SoxRS by RT-PCR in strains with interest encoding gene knock-out, and eliminate the regulation of RamA, MarA and SoxRS on expression of AcrAB-TolC and cross talk between these globle regulators including RamA, MarA, SoxRS.