Impact of siderophore production on Pseudomonas aeruginosa infections in immunosuppressed mice

Pseudomonas aeruginosa produces siderophores, pyoverdin and pyochelin, for high-affinity iron uptake. To investigate their contribution to P. aerugino sa infections, we constructed allelic exchange mutants from strain PAO1 whi ch were deficient in producing one or both of the siderophores. When inocul ated into the calf muscles of immunosuppressed mice, pyochelin-deficient an d pyoverdin-deficient mutants grew and killed the animals as efficiently as PAO1. In contrast, the pyochelin- and pyoverdin-deficient (double) mutant did not show lethal virulence? although it did infect the muscles. On the o ther hand, when inoculated intranasally, all mutants grew in the lungs and killed immunosuppressed mice. Compared with PAO1, however, the pyoverdin-de ficient mutant and the double mutant grew poorly in the lungs, and the latt er was significantly attenuated for virulence. Irrespective of the inoculat ion route, the pyoverdin-deficient and doubly deficient mutants detected in the blood were significantly less numerous than PAO1, Additionally, in vit ro examination demonstrated that the growth of the double mutant was extrem ely reduced under a free-iron-restricted condition with apotransferrin but that the growth reduction was completely canceled by supplementation with h emoglobin as a heme source. These results suggest that both pyoverdin and p yochelin are required far efficient bacterial growth and full expression of virulence in P. aeruginosa infection, although pyoverdin may be comparativ ely more important for bacterial growth and dissemination. However, the sid erophores were not always required for infection, It is possible that non-s iderophore-mediated iron acquisition, such as via heme uptake, might also p lay an important role in P. aeruginosa infections.