Copper toxicity towards Campylobacter jejuni is enhanced by the nickel chelator dimethylglyoxime

The nickel (Ni)-chelator dimethylglyoxime (DMG) was found to be bacteriostatic towards Campylobacter jejuni. Supplementation of nickel to DMG-containing media restored bacterial growth, whereas supplementation of cobalt or zinc had no effect on the growth inhibition. Unexpectedly, the combination of millimolar levels of DMG with micromolar levels of copper (Cu) was bactericidal, an effect not seen in select Gram-negative pathogenic bacteria. Both the cytoplasmic Ni-binding chaperone SlyD and the twin arginine translocation (Tat)-dependent periplasmic copper oxidase CueO were found to play a central role in the Cu-DMG hypersensitivity phenotype. Ni-replete SlyD is needed for Tat-dependent CueO translocation to the periplasm, whereas Ni-depleted (DMG-treated) SlyD is unable to interact with the CueO Tat signal peptide, leading to mislocalization of CueO and increased copper sensitivity. In support of this model, C. jejuni ΔslyD and ΔcueO mutants were more sensitive to copper than the wild-type (WT); CueO was less abundant in the periplasmic fraction of ΔslyD or DMG-grown WT cells, compared to WT cells grown on plain medium; SlyD binds the CueO signal sequence peptide, with DMG inhibiting and nickel enhancing the binding, respectively. Injection of Cu-DMG into Galleria mellonella before C. jejuni inoculation significantly increased the insect survival rate compared to the control group. In chickens, oral administration of DMG or Cu-DMG decreased and even abolished C. jejuni colonization in some cases, compared to both water-only and Cu-only control groups. The latter finding is important, since campylobacteriosis is the leading bacterial foodborne infection, and chicken meat constitutes the major foodborne source.