title: Molecular characterization of the PhoPQ-PmrD-PmrAB mediated pathway regulating polymyxin B resistance in Klebsiella pneumoniae CG43.
abstract: BACKGROUND
  The cationic peptide antibiotic polymyxin has recently been reevaluated in the treatment of severe infections caused by gram negative bacteria.
  
  
  METHODS
  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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Biological Science and Technology, National Chiao-Tung University, Hsin Chu, Taiwan, China.
authors.forename: Hsin-Yao
authors.initials: HY
authors.lastname: Cheng
authors.forename: Yi-Fong
authors.initials: YF
authors.lastname: Chen
authors.forename: Hwei-Ling
authors.initials: HL
authors.lastname: Peng
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000378:metabolism*; D002460:Cell Line; D003001:Cloning, Molecular; D004352:Drug Resistance, Microbial / Q000502:physiology*; D024202:Electrophoretic Mobility Shift Assay; D007711:Klebsiella pneumoniae / Q000502:physiology*; D051379:Mice; D011112:Polymyxin B / Q000494:pharmacology*; D020798:Two-Hybrid System Techniques
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; C081902:pmrA protein, Bacteria; C061064:PhoP protein, Bacteria; D011112:Polymyxin B