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. | Cheng et al. Journal of Biomedical Science 2010 17 60 http content 17 1 60 tì NSC The cost of publication in Journal of Biomedical Science Is borne by the National Science Council Taiwan JOURNAL OF BIOMEDICAL SCIENCE RESEARCH Open Access Molecular characterization of the PhoPQ-PmrD-PmrAB mediated pathway regulating polymyxin B resistance in Klebsiella pneumoniae CG43 Hsin-Yao Cheng1 Yi-Fong Chen2 Hwei-Ling Peng1 2 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
