Department of Medical Biochemistry and Microbiology, Uppsala University, Uppsala, Sweden.
Department of Medical Biochemistry and Microbiology, Uppsala University, Uppsala, Sweden
Antimicrob Agents Chemother. 2019 Sep 23;63(10). doi: 10.1128/AAC.00612-19. Print 2019 Oct.
Mecillinam (amdinocillin) is a β-lactam antibiotic that inhibits the essential penicillin-binding protein 2 (PBP2). In clinical isolates of from urinary tract infections, inactivation of the gene (which encodes the main regulator of cysteine biosynthesis, CysB) is the major cause of resistance. How a nonfunctional CysB protein confers resistance is unknown, however, and in this study we wanted to examine the mechanism of resistance. Results show that mutations cause a gene regulatory response that changes the expression of ∼450 genes. Among the proteins that show increased levels are the PBP1B, LpoB, and FtsZ proteins, which are known to be involved in peptidoglycan biosynthesis. Artificial overexpression of either PBP1B or LpoB in a wild-type strain conferred mecillinam resistance; conversely, inactivation of either the gene (which encodes PBP1B) or the gene (which encodes the PBP1B activator LpoB) made mutants susceptible. These results show that expression of the proteins PBP1B and LpoB is both necessary and sufficient to confer mecillinam resistance. The addition of reducing agents to a mutant converted it to full susceptibility, with associated downregulation of PBP1B, LpoB, and FtsZ. We propose a model in which mutants confer mecillinam resistance by inducing a response that causes upregulation of the PBP1B and LpoB proteins. The higher levels of these two proteins can then rescue cells with mecillinam-inhibited PBP2. Our results also show how resistance can be modulated by external conditions such as reducing agents.
美西林（氨曲南）是一种β-内酰胺抗生素，可抑制必需的青霉素结合蛋白 2（PBP2）。在尿路感染的 临床分离株中， 基因（编码半胱氨酸生物合成的主要调节剂 CysB）的失活是耐药的主要原因。然而，无功能 CysB 蛋白如何赋予耐药性尚不清楚，在本研究中，我们希望研究耐药机制。结果表明， 突变导致基因调控反应，改变了约 450 个基因的表达。在表达水平升高的蛋白质中，有 PBP1B、LpoB 和 FtsZ 蛋白，它们已知参与肽聚糖生物合成。在野生型 菌株中人工过表达 PBP1B 或 LpoB 均可赋予美西林耐药性；相反， 基因（编码 PBP1B）或 基因（编码 PBP1B 激活剂 LpoB）的失活使 突变体易感性。这些结果表明，PBP1B 和 LpoB 蛋白的表达对于赋予美西林耐药性是必需和充分的。向 突变体中添加还原剂可使其完全易感性，同时下调 PBP1B、LpoB 和 FtsZ。我们提出了一个模型，其中 突变体通过诱导导致 PBP1B 和 LpoB 蛋白上调的反应来赋予美西林耐药性。然后，这两种蛋白的更高水平可以挽救被美西林抑制的 PBP2 的细胞。我们的结果还表明，耐药性可以通过还原剂等外部条件进行调节。
