Stepwise upregulation of the Pseudomonas aeruginosa chromosomal cephalosporinase conferring high-level β-lactam resistance involves three AmpD homologues
Stepwise upregulation of the Pseudomonas aeruginosa chromosomal cephalosporinase conferring high-level β-lactam resistance involves three AmpD homologues
复制标题
DOI：
10.1128/aac.50.5.1780-1787.2006
复制
发表时间：
2006-05-01
影响因子：
4.9
通讯作者：
Oliver, A
中科院分区：
文献类型：
--
作者：
Juan, C;Moyá, B;Oliver, A
由染色体头孢菌素酶AmpC的过度产生介导的对抗假单胞菌青霉素和头孢菌素的耐药性的发展是铜绿假单胞菌感染成功治疗的主要威胁。尽管先前已发现ampD失活导致部分去阻遏表型，其特征在于AmpC产生增加但保留进一步诱导，但铜绿假单胞菌中ampC的调节远未被充分理解。我们证明，ainpC的表达是协调抑制由三个AmpD同系物，包括先前描述的蛋白质AmpD加上两个额外的蛋白质，指定AmpDh 2和AmpDh 3。三个AmpD同源物负责逐步ampC上调机制，最终导致染色体头孢菌素酶的组成性超表达和高水平的抗假单胞菌P-内酰胺抗性，如通过分析三个单ampD突变体，三个双ampD突变体和三重ampD突变体所示。这是通过三步升级机制实现的，呈现四种相关的表达状态：基础水平诱导表达（野生型），中度过度诱导表达，抗假单胞菌β-内酰胺耐药性增加（ampD突变体），高水平超不溶性表达伴高水平β-内酰胺耐药（ampD ampDh 3双突变体）和非常高水平（与野生型相比超过1，000倍）的去阻遏表达（三突变体）。虽然一步诱导-去阻遏表达模型在天然抗性机制中很常见，但这是第一个表征的实例，其中抗性基因的表达可以通过多个去阻遏步骤顺序扩增。
Development of resistance to the antipseudomonal penicillins and cephalosporins mediated by hyperproduction of the chromosomal cephalosporinase AmpC is a major threat to the successful treatment of Pseudomonas aeruginosa infections. Although ampD inactivation has been previously found to lead to a partially derepressed phenotype characterized by increased AmpC production but retaining further inducibility, the regulation of ampC in P. aeruginosa is far from well understood. We demonstrate that ainpC expression is coordinately repressed by three AmpD homologues, including the previously described protein AmpD plus two additional proteins, designated AmpDh2 and AmpDh3. The three AmpD homologues are responsible for a stepwise ampC upregulation mechanism ultimately leading to constitutive hyperexpression of the chromosomal cephalosporinase and high-level antipseudomonal P-lactam resistance, as shown by analysis of the three single ampD mutants, the three double ampD mutants, and the triple ampD mutant. This is achieved by a three-step escalating mechanism rendering four relevant expression states: basal-level inducible expression (wild type), moderate-level hyperinducible expression with increased antipseudomonal beta-lactam resistance (ampD mutant), high-level hyperinclucible expression with high-level beta-lactam resistance (ampD ampDh3 double mutant), and very high-level (more than 1,000-fold compared to the wild type) derepressed expression (triple mutant). Although one-step inducible-derepressed expression models are frequent in natural resistance mechanisms, this is the first characterized example in which expression of a resistance gene can be sequentially amplified through multiple steps of derepression.