To human health worldwide. Existing treatments are becoming inefficacious and therefore there is an urgent need for the development of treatments with alternative modes of action. The use of gallium as an antimicrobial agent has been of interest due to its unconventional mode of action involving the inhibition of iron acquisition and metabolism. The structural similarity and inability to reduce from a trivalent to divalent form under normal physiological conditions allows gallium to act as an iron mimetic and inhibit many iron-dependent biological pathways, respectively. The antimicrobial potential of gallium maltolate (GaM), Ga(III) coordination complex of maltol, was investigated on the opportunistic pathogen Pseudomonas aeruginosa. In vitro and in vivo analyses using Galleria mellonella (greater wax moth) larvae demonstrated the potent bacteriostatic and non-toxic effect of the complex. Subsequent analysis of GaM treated P. aeruginosa via label-free quantitative proteomics provided an insight into the intrinsic mechanisms of action of GaM. Increased expression of iron-storage protein Bacterioferritin B, the HemO component of iron-sulfur clusters and several stress response proteins (Chaperone Proteins ClpB, HtpG and DnaJ) indicate cell stress in response to inhibited iron uptake. Decreased expression of LasA Protease and LasB Elastase quorum-sensing proteins and flagellar motility proteins FlgM and FlgG further demonstrate the growth inhibitory effect of GaM. These findings provide a basis for a better understanding of the mode of action of GaM, a requirement for the improvement of synthesis and efficacy of the treatment.
