病原菌超广谱β-内酰胺酶（ESBL）表达量决定其耐药水平。我们近期研究证实ESBL表达量在核酸序列完全相同的细菌间存在差异，并与细菌生长速率相关，且可随抗生素浓度变化而变化，从而提高了细菌耐药适应性，但其机制尚不明确。四/五磷酸鸟苷[(p)ppGpp] 参与调节多种基因表达，且是细菌生长速率的重要调控因子。我们推测(p)ppGpp通过调节ESBL表达量提高细菌的耐药适应性。本课题拟收集肺部感染来源产ESBL临床菌株，构建携带有ESBL/GFP荧光表达载体的实验菌株，探讨临床和实验菌株ESBL表达量与(p)ppGpp的关系；通过构建(p)ppGpp合成酶基因relA/spot双缺失菌株，研究(p)ppGpp 缺失情况下细菌ESBL表达模式及对抗生素的适应能力，并比较双缺失菌株与野生菌株的差异，以深入了解ESBL差异表达机制，为深入认识细菌耐药、寻求新的抗生素靶点提供策略和思路。

The resistance level to β-lactam agents in ESBL-producing bacteria is positively correlated with the expression level of ESBL genes. Our previous study found the existence of cell-to-cell variation in expression of ESBL genes in single clonal population and the expression level of ESBL genes was increasing with increment of the extracellular ceftriaxone concentration as well as correlated with growth rate of bacteria. The heterogenous expression model of ESBL genes was identified as an important mechanism that bacteria developed to high resistance and adapted to antibiotic stresses. (p)ppGpp which is an important regulator of growth rate of bacteria mediates the expression of many genes of bacteria. We infer that (p)ppGpp can help bacteria develop to high resistance and adapt to antibiotic stresses through mediating the expression of ESBL genes. So, in this study, we intend to 1）collect ESBL-producing bacteria isolates responsible for pneumonia and construct experimental strains carrying the ESBL/GFP, then explore the relationship between concentration of (p)ppGpp and the expression level of ESBL genes; 2) introduce mutants of (p)ppGpp-deficient cells △relA/spot by mutating of relA and spot, the products of which were the (p)ppGpp synthetase, then measure the ESBL expression model of △relA/spot as well as the ability of △relA/spot to fight against the fluctuating stresses of antibiotic, meanwhile compare the differences between △relA/spot and the wild strain. This will contribute to understand the detailed mechanisms of heterogeneous expression of ESBL genes and the mechanisms of resistance of bacteria as well as put forward an innovative theory for developing new antibiotics.