Bacterial Iron Metabolism and Immunity to Pasteurella septica and Escherichia coli

Abstract

IRON is essential for bacterial growth¹, and there is now sufficient evidence to suggest that the ability to acquire iron may be an essential feature of pathogenicity^2–5. Conversely, the ability of the host to prevent the uptake of iron by bacteria may constitute an important means of defence against certain infections^2–4. Iron compounds can greatly reduce host resistance. The protection normally provided against Clostridium welchii type A by specific antiserum is abolished by injection of iron immediately before infection⁴. Similar results were obtained with a highly virulent strain of Pasteurella septica where a variety of iron compounds completely abolished the protective power of specific antiserum⁶. In both cases the ability of antiserum to suppress bacterial growth was removed, with the result that bacterial growth in iron-treated animals given antiserum was identical to that seen in unimmunized controls^4,6. Iron compounds greatly enhance the virulence of Escherichia coli for guinea-pigs, the lethal dose being reduced by approximately 100,000-fold. In this case the normal ability to suppress bacterial growth is lost, the animals dying from an overwhelming infection with doses of bacteria that are normally harmless³.