MECHANISMS OF SULFONAMIDE RESISTANCE IN E. COLI

磺酰胺类抗生素可阻止还原型 通过抑制H2蝶酸的产生的叶酸化合物 从6-羟甲基蝶呤焦磷酸和p- 氨基苯甲酸酯（PABA）。 一种常见的抵抗模式， 磺胺类抗生素在E.大肠杆菌是通过突变 编码H2蝶酸合酶的结构基因， 改变的酶产物是磺酰胺抗性形式， 更有效地区分PABA和磺胺 比野生型酶更强 磺胺抗性 由许多分离自 多重耐药临床E. 大肠杆菌菌株是由 相同的机制：磺胺抗性的表达 H2蝶酸合酶。 然而，我已经证明磺胺 E.大肠杆菌中可以通过基因扩增来介导。 虽然我还没有确定放大器的身份 基因，编码H2蝶酸合酶的基因是一个主基因， 候选者，因为该基因产物是磺酰胺靶 抑制作用 我这种磺胺类药物耐药菌株 表征具有8倍串联扩增的DNA片段， 18 kb的长度。 插入序列（IS5）的关联 扩增DNA的一个（或两个）端点表明 位点特异性（非法）重组的作用。 此事件 与其他非法扩增不同， 与IS序列无关。 本申请建议 确定基因扩增事件的机制，以及 以表征H2蝶酸合酶的结构、功能和 在基因水平上的表达。

Sulfonamide antibiotics prevent the biosynthesis of reduced folate compounds by inhibiting the production of H2pteroate from 6-hydroxymethylpterin pyrophosphate and p- aminobenzaoate (PABA). A common mode of resistance to sulfonamide antibiotics in E. coli is via mutation of the structural gene encoding H2pteroate synthase, so that the altered enzyme product is a sulfonamide resistant form that discriminates more effectively between PABA and sulfonamides than does the wild type enzyme. Sulfonamide resistance conferred by many R-determinant plasmids isolated from multiple antibiotic resistant clinical E. coli strains is by the same mechanism: expression of a sulfonamide resistant H2pteroate synthase. However, I have shown that sulfonamide resistance in E. coli can be mediated by gene amplification. Although I have not yet determined the identity of the amplified gene, the gene encoding H2pteroate synthase is a prime candidate, since that gene product is the target of sulfonamide inhibition. The sulfonamide resistant strain that I am characterizing has an 8-fold tandemly amplified DNA segment 18 kb in length. The association of an insertion sequence (IS5) with one (or both) endpoints of the amplified DNA suggests a role for site specific (illegitimate) recombination. This event is distinct from other illegitimate amplifications that seem to be independent of IS sequences. This application proposes to determine the mechanism of the gene amplification event, and to characterize H2pteroate synthase structure, function and expression at the genetic level.