Escherichia colicells containing the plasmid ColV produce the iron ionophore aerobactin

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The first colicin to be described (colicin V) in 1925 was the product of a virulent Escherichia coli strain [1]. Since then studies have been performed with the aim of identifying the virulence factor associated with the ability to produce colicin V. ' Such a relationship has been established for humans, domestic animals and in experimental animal systems infected with pathogenic E. coli strains [2-7]. To date it is clear that several virulence enhancing factors are encoded by ColV plasmids. Synthesis of colicin V seems not to be essential for virulence enhancement [2,3] although it has been reported that colicin V inhibits macrophages [8]. E. coli strains harbouring ColV plasmids show an enhanced resistance to the bactericidal effects of serum [3,9], and their growth is supported by a new iron sequestering system [7,10,11]. It was shown that the iron ligand was of the hydroxamate type but ferrichrome, the only known ferric hydroxamate complex to be actively taken up by E. coli, was excluded [11 ]. In this paper it is reported that aerobactin is the new iron ligand produced by ColV-bearing E. coli strains. The search for the iron ligand was guided by the fact that other Enterobacteriaceae, Aerobacter aerogenes [12], Shigella flexneri [13] and Enterobacter cloacae [14] produce aerobactin. A new rapid isolation procedure was developed which is different from the one described by the discoverers of aerobactin, F. Gibson and D.I. Magrath [12], and which allows the isolation of large quantities in highly pure form.