Most enterobacteria obtain the
iron they require for growth by producing low-molecular-weight high-affinity
iron ligands known as
siderophores. These substances chelate and solubilize
iron making it available to bacteria. The pathogenic Yersiniae produce no detectable
siderophores; thus, they proliferate poorly or not at all under conditions of
iron limitation. Most systemic
infections with Yersinia enterocolitica occur in patients who are overloaded with
iron. This may be due to the presence of excess
iron in the tissues of such patients, but the adverse effects of excess
iron on immune responsiveness may also be partly responsible. Many patients with
iron overload receive treatment with
desferrioxamine B, a bacterial
siderophore which promotes growth of Y. enterocolitica in vitro and in vivo. Thus,
desferrioxamine B may add to the risk of systemic
yersiniosis developing in patients with
siderosis. Some strains of Yersinia frederiksenii, Yersinia intermedia and Yersinia kristensenii produce the hydroxamate
siderophore aerobactin, but, paradoxically, they appear to be unable to proliferate in tissues.