title: Role of RppA in the regulation of polymyxin b susceptibility, swarming, and virulence factor expression in Proteus mirabilis.
abstract: Proteus mirabilis, a human pathogen that frequently causes urinary tract infections, is intrinsically highly resistant to cationic antimicrobial peptides, such as polymyxin B (PB). To explore the mechanisms underlying P. mirabilis resistance to PB, a mutant which displayed increased (> 160-fold) sensitivity to PB was identified by transposon mutagenesis. This mutant was found to have Tn5 inserted into a novel gene, rppA. Sequence analysis indicated that rppA may encode a response regulator of the two-component system and is located upstream of the rppB gene, which may encode a membrane sensor kinase. An rppA knockout mutant of P. mirabilis had an altered lipopolysaccharide (LPS) profile. The LPS purified from the rppA knockout mutant could bind more PB than the LPS purified from the wild type. These properties of the rppA knockout mutant may contribute to its PB-sensitive phenotype. The rppA knockout mutant exhibited greater swarming motility and cytotoxic activity and expressed higher levels of flagellin and hemolysin than the wild type, suggesting that RppA negatively regulates swarming, hemolysin expression, and cytotoxic activity in P. mirabilis. PB could modulate LPS synthesis and modification, swarming, hemolysin expression, and cytotoxic activity in P. mirabilis through an RppA-dependent pathway, suggesting that PB could serve as a signal to regulate RppA activity. Finally, we demonstrated that the expression of rppA was up-regulated by a low concentration of PB and down-regulated by a high concentration of Mg2+. Together, these data highlight the essential role of RppA in regulating PB susceptibility and virulence functions in P. mirabilis.
authors.affiliation: Graduate Institute of Clinical Laboratory Sciences and Medical Biotechnology, College of Medicine, National Taiwan University, Taipei, Taiwan, Republic of China.
authors.forename: Won-Bo
authors.initials: WB
authors.lastname: Wang
authors.forename: I-Chun
authors.initials: IC
authors.lastname: Chen
authors.forename: Sin-Sien
authors.initials: SS
authors.lastname: Jiang
authors.forename: Hui-Ru
authors.initials: HR
authors.lastname: Chen
authors.forename: Chia-Yu
authors.initials: CY
authors.lastname: Hsu
authors.forename: Po-Ren
authors.initials: PR
authors.lastname: Hsueh
authors.forename: Wei-Bin
authors.initials: WB
authors.lastname: Hsu
authors.forename: Shwu-Jen
authors.initials: SJ
authors.lastname: Liaw
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001426:Bacterial Proteins / Q000502:physiology*; D002460:Cell Line; D004251:DNA Transposable Elements; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D024881:Drug Resistance, Bacterial; D005408:Flagellin / Q000096:biosynthesis; D017353:Gene Deletion; D015964:Gene Expression Regulation, Bacterial; D006460:Hemolysin Proteins / Q000096:biosynthesis; D006801:Humans; D008070:Lipopolysaccharides / Q000032:analysis / Q000302:isolation & purification / Q000378:metabolism; D008124:Locomotion; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D011112:Polymyxin B / Q000378:metabolism / Q000494:pharmacology*; D011513:Proteus mirabilis / Q000737:chemistry / Q000187:drug effects / Q000502:physiology*; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D019459:Urothelium / Q000382:microbiology; D037521:Virulence Factors / Q000096:biosynthesis*
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D004251:DNA Transposable Elements; D004269:DNA, Bacterial; D006460:Hemolysin Proteins; D008070:Lipopolysaccharides; C412036:RppA protein, Synechocystis; D037521:Virulence Factors; D005408:Flagellin; D011112:Polymyxin B