Department of Biological Science and Technology, National Chiao-Tung University, Hsin Chu, Taiwan, China.
J Biomed Sci. 2010 Jul 24;17(1):60. doi: 10.1186/1423-0127-17-60.
The cationic peptide antibiotic polymyxin has recently been reevaluated in the treatment of severe infections caused by gram negative bacteria.
In this study, the genetic determinants for capsular polysaccharide level and lipopolysaccharide modification involved in polymyxin B resistance of the opportunistic pathogen Klebsiella pneumoniae were characterized. The expressional control of the genes responsible for the resistance was assessed by a LacZ reporter system. The PmrD connector-mediated regulation for the expression of pmr genes involved in polymyxin B resistance was also demonstrated by DNA EMSA, two-hybrid analysis and in vitro phosphor-transfer assay.
Deletion of the rcsB, which encoded an activator for the production of capsular polysaccharide, had a minor effect on K. pneumoniae resistance to polymyxin B. On the other hand, deletion of ugd or pmrF gene resulted in a drastic reduction of the resistance. The polymyxin B resistance was shown to be regulated by the two-component response regulators PhoP and PmrA at low magnesium and high iron, respectively. Similar to the control identified in Salmonella, expression of pmrD in K. pneumoniae was dependent on PhoP, the activated PmrD would then bind to PmrA to prolong the phosphorylation state of the PmrA, and eventually turn on the expression of pmr for the resistance to polymyxin B.
The study reports a role of the capsular polysaccharide level and the pmr genes for K. pneumoniae resistance to polymyxin B. The PmrD connector-mediated pathway in governing the regulation of pmr expression was demonstrated. In comparison to the pmr regulation in Salmonella, PhoP in K. pneumoniae plays a major regulatory role in polymyxin B resistance.
阳离子肽抗生素多粘菌素最近在治疗由革兰氏阴性菌引起的严重感染方面得到了重新评估。
在这项研究中，我们描述了机会性病原体肺炎克雷伯菌中多粘菌素 B 耐药性相关的荚膜多糖水平和脂多糖修饰的遗传决定因素。通过 LacZ 报告系统评估了与耐药性相关基因的表达调控。通过 DNA EMSA、双杂交分析和体外磷转移测定，还证明了 PmrD 连接器介导的多粘菌素 B 耐药性相关 pmr 基因表达调控。
rcsB 基因缺失（编码荚膜多糖产生的激活因子）对肺炎克雷伯菌多粘菌素 B 的耐药性仅有轻微影响。另一方面，ugd 或 pmrF 基因的缺失导致耐药性大幅降低。研究表明，在低镁和高铁条件下，PhoP 和 PmrA 这两个两元组反应调节剂分别调节多粘菌素 B 的耐药性。与沙门氏菌中的控制机制相似，肺炎克雷伯菌中 pmrD 的表达依赖于 PhoP，激活的 PmrD 与 PmrA 结合，延长 PmrA 的磷酸化状态，最终开启 pmr 基因的表达，从而对多粘菌素 B 产生耐药性。
本研究报告了肺炎克雷伯菌对多粘菌素 B 耐药性的荚膜多糖水平和 pmr 基因的作用。证明了 PmrD 连接器介导的途径在调控 pmr 表达中的作用。与沙门氏菌中的 pmr 调控相比，肺炎克雷伯菌中的 PhoP 在多粘菌素 B 耐药性中发挥主要调控作用。
