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 Bsusceptible 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 b-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.

No effects without causes: the Iron Dysregulation and Dormant Microbes hypothesis for chronic, inflammatory diseases

“…In consequence, the likelihood of infection is greatly enhanced when free iron levels are raised (Boyanova, ; Braun, ; Eichhorn et al ., ; Ishida & Johansen, ; Mittal et al ., ; Nevitt, ; Ngok‐Ngam et al ., ; Rodriguez & Smith, ; Sritharan, ; Su et al ., ; Sutak et al ., ; Vasil & Ochsner, ), and indeed the ‘virulence’ of microbes is strongly correlated with their expression of siderophore (iron‐binding) or iron transporter (Do, Zafar & Saier Jr, ; Tang & Saier Jr, ) genes. In addition, siderophores can act directly to induce cytokine expression (Holden et al ., ).…”

Molecular mechanisms of polymyxin resistance and detection of mcr genes

“…All these findings are carefully described in Trimble et al 2 . It is also worth mentioning that a ferrous iron-binding protein, outer membrane protein (Omb) with unclear biological role, caused alterations in the bacterial surface charge that decreased affinity to antimicrobial peptides and increased resistance to polymyxin B in S. enterica 19 .…”

Partial Associations of Dietary Iron, Smoking and Intestinal Bacteria with Colorectal Cancer Risk

“…Some of these irontrophic bacteria, such as Salmonella , produce bacterial toxins that exert genotoxicity and have been linked to biliary tract cancer (12). In addition, Salmonella are known to use multiple high-affinity iron acquisition systems (13,14). …”