Evaluation with an iuc::Tn10 mutant of the role of aerobactin production in the virulence of Shigella flexneri

Abstract

To evaluate the role of aerobactin production in the virulence of Shigella flexneri, a iuc::Tn10 insertion mutant was obtained from strain M90T, a serotype 5 isolate. This mutant was tested for its ability to invade and kill HeLa cells in monolayers, to elicit keratoconjunctivitis in guinea pigs, and to infect ligated segments of rabbit ileal loops. Although this mutant did not grow in iron-depleted media, its ability to grow intracellularly and eventually kill HeLa cells was unchanged from that of the wild-type strain. On the other hand, an inoculum-dependent effect was observed in the Sereny test, as well as in the rabbit ligated ileal loop model, which was monitored for fluid production and for both gross and microscopical alterations of the mucosa. Transduction of the mutation within a noninvasive plasmidless derivative of the parental strain did not alter growth within the intestinal lumen. We conclude that aerobactin production most probably provides invasive strains with a selective advantage for growth within tissues when located in extracellular compartments.