title: Ferrous iron-binding protein Omb of Salmonella enterica serovar Choleraesuis promotes resistance to hydrophobic antibiotics and contributes to its virulence.
abstract: Salmonella enterica serovar Choleraesuis (SC) is an important enteric pathogen that causes serious systemic infections in swine and humans. To identify the genes required for resistance to antimicrobial peptides, we constructed a bank of SC transposon mutants and screened them for hypersensitivity to the cationic peptide polymyxin B. Here we report one isolated polymyxin B-susceptible mutant that also exhibited increased sensitivity toward human neutrophil peptide alpha-defensin 1 (HNP-1) and hydrophobic antibiotics including erythromycin and novobiocin. The mutant had a mutation in an ORF identified as outer membrane beta-barrel protein gene omb. The purified recombinant Omb protein was characterized as a ferrous iron-binding protein. The constructed omb isogenic mutant grew more slowly in iron-limiting conditions than the wild-type (WT) parent strain. In addition, compared with the WT strain, the omb mutant exhibited an increase in net negative charge upon the cell surface and was more easily killed by polymyxin B, HNP-1 and hydrophobic antibiotics. The omb gene was transcribed, regardless of the iron content within the growth medium, and the Omb protein appeared exclusively in the outer membrane fraction. Infection experiments demonstrated virulence attenuation when the mutant was administered orally or intraperitoneally to mice. This study indicates that Omb is a previously unrecognized ferrous iron-binding protein. In vivo, Omb may be involved in the acquisition of ferrous iron during the initial stages of SC infection and appears to be an important virulence factor for SC in mice.
authors.affiliation: Department of Life Science, College of Bioscience and Biotechnology, National Cheng-Kung University, No. 1, University Road, Tainan 701, Taiwan, ROC.|Department of Biotechnology, Chia-Nan University of Pharmacy and Science, 60, Erh-Jen Rd, Sec.1, Jen-Te, Tainan 717, Taiwan, ROC.
authors.forename: Jer-Horng
authors.initials: JH
authors.lastname: Su
authors.affiliation: Department of Medical Research, Chi Mei Medical Center, No. 901, Chung Hwa Road, Yong Kang City, Tainan 710, Taiwan, ROC.
authors.forename: Yin-Ching
authors.initials: YC
authors.lastname: Chung
authors.affiliation: Department of Internal Medicine, National Cheng-Kung University Hospital, No. 138, Sheng Li Road, Tainan 701, Taiwan, ROC.
authors.forename: Hsin-Chun
authors.initials: HC
authors.lastname: Lee
authors.affiliation: Department of Life Science, College of Bioscience and Biotechnology, National Cheng-Kung University, No. 1, University Road, Tainan 701, Taiwan, ROC.
authors.forename: I-Cheng
authors.initials: IC
authors.lastname: Tseng
authors.affiliation: Research Institute of Biotechnology, Hungkuang University, No. 34, Chung-Chie Rd, Sha Lu, Taichung County, Taiwan 43302, ROC.|Sustainable Environment Research Center, National Cheng-Kung University, Tainan 701, Taiwan, ROC.|Department of Biochemistry and Molecular Biology, College of Medicine, National Cheng-Kung University, Tainan 701, Taiwan, ROC.
authors.forename: Ming-Chung
authors.initials: MC
authors.lastname: Chang
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D024881:Drug Resistance, Bacterial / Q000235:genetics*; D004917:Erythromycin / Q000494:pharmacology; D006801:Humans; D007501:Iron / Q000378:metabolism*; D051379:Mice; D008807:Mice, Inbred BALB C; D008969:Molecular Sequence Data; D009675:Novobiocin / Q000494:pharmacology; D011112:Polymyxin B / Q000494:pharmacology; D019779:Salmonella enterica / Q000187:drug effects / Q000378:metabolism / Q000472:pathogenicity; D014774:Virulence; D023084:alpha-Defensins / Q000494:pharmacology
chemical_list: D000900:Anti-Bacterial Agents; D001425:Bacterial Outer Membrane Proteins; D023084:alpha-Defensins; C406413:human neutrophil peptide 1; D009675:Novobiocin; D004917:Erythromycin; D007501:Iron; D011112:Polymyxin B