Chromosomal‐encoded siderophores are required for mouse virulence of enteropathogenic Yersinia species

Yersinia enterocolitica and Y. pseudotuberculosis are enteropathogenic for humans. Essential virulence functions of these pathogens are determined by a 40‐mDa plasmid. Plasmid‐bearing Y. pseudotuberculosis strains and Y. enterocolitica strains of serotypes 0 : 8, 0 : 13, 0 : 20 and 0 : 40 are lethal for mice. In contrast, human pathogenic Y. enterocolitica strains of serotype 0 : 3, 0 : 9 and 0 : 5.27 are not mouse‐lethal. Using a sensitive siderophore‐indicator CAS‐agar, we were able to detect siderophore production in all mouse‐lethal Y. enterocolitica and Y. pseudotuberculosis strains mentioned above. By Tn5‐transposon insertions into the chromosome of a serotype 0 : 8 strain we obtained two siderophore‐deficient mutants. Introduction of the virulence plasmid did not render these mutants mouse‐lethal, indicating that siderophore production is an essential virulence factor. The human nonpathogenic, aerobactin‐producing strains of Y. intermedia, Y. kristensenii and Y. frederiksenii remained avirulent for mice after receiving the virulence plasmid of Y. enterocolitica. Obviously the siderophore aerobactin does not contribute to virulence in the genus Yersinia.