Iron/Heme Metabolism-Targeted Gallium(III) Nanoparticles Are Active against Extracellular and Intracellular Pseudomonas aeruginosa and Acinetobacter baumannii

Iron/heme acquisition systems are critical for microorganisms to acquire iron from the human host, where iron sources are limited due to the nutritional immune system and insolubility of the ferric form of iron. Prior work has shown that a variety of gallium compounds can interfere with bacterial iron acquisition. This study explored the intra- and extracellular antimicrobial activities of gallium protoporphyrin (GaPP), gallium mesoporphyrin (GaMP), and nanoparticles encapsulating GaPP or GaMP against the Gram-negative pathogens Pseudomonas aeruginosa and Acinetobacter baumannii, including clinical isolates. All P. aeruginosa and A. baumannii isolates were susceptible to GaPP and GaMP, with MICs ranging from 0.5 to ∼32 μg/ml in iron-depleted medium. Significant intra- and extracellular growth inhibition was observed against P. aeruginosa cultured in macrophages at a gallium concentration of 3.3 μg/ml (5 μM) of all Ga(III) compounds, including nanoparticles. Nanoparticle formulations showed prolonged activity against both P. aeruginosa and A. baumannii in previously infected macrophages. When the macrophages were loaded with the nanoparticles 3 days prior to infection, there was a 5-fold decrease in growth of P. aeruginosa in the presence of single emulsion F127 copolymer nanoparticles encapsulating GaMP (eFGaMP). In addition, all Ga(III) porphyrins and nanoparticles showed significant intracellular and antibiofilm activity against both pathogens, with the nanoparticles exhibiting intracellular activity for 3 days. Ga nanoparticles also increased the survival rate of Caenorhabditis elegans nematodes infected by P. aeruginosa and A. baumannii. Our results demonstrate that Ga nanoparticles have prolonged in vitro and in vivo activities against both P. aeruginosa and A. baumannii, including disruption of their biofilms.