Utilization of iron-catecholamine complexes involving ferric reductase activity in Listeria monocytogenes

Listeria monocytogenes is a ubiquitous potentially pathogenic organism requiring iron for growth and virulence, Although ii does not produce siderophores, L. monocytogenes is able to obtain iron by using either exogenous siderophores produced by various microorganisms or natural catechol compounds widespread in the environment, In the presence of tropolone, an iron-chelating agent, growth of L. monocytogenes is completely inhibited. However, the growth inhibition fan be relieved by the addition of dopamine or norepinephrine under their different isomeric forms, while the catecholamine derivatives 4-hydroxy-3-methoxyphenylglycol and normetanephrine did not relieve the inhibitory effect of tropolone. Preincubation of L. monocytogenes with chlorpromazine and yohimbine did not antagonize the growth-promoting effect of catecholamines in iron-complexed medium. In addition, norepinephrine stimulated the growth-promoting effect induced by human transferrin in iron-limited medium. Furthermore, dopamine and norepinephrine allowed Fe-55 uptake lay iron-deprived bacterial cells. The uptake Of icon was energy dependent, as indicated by inhibition of Fe-55 uptake at 0 degrees C as well as by preincubating the bacteria with KCN. Inhibition of Fe-55 uptake by L. monocytogenes was also observed in the presence of Pt(II). Moreover, when assessed by a whole-cell ferric reductase assay, reductase activity of L. monocytogenes was inhibited by Pt(II). These data demonstrate that dopamine and norepinephrine can function as siderophore-like compounds in L. monocytogenes owing to their ortho-diphenol function and that catecholamine-mediated iron acquisition does not involve specific catecholamine receptors but acts through a cell-bound ferrireductase activity.