Iron and virulence of Haemophilus ducreyi in a primate model

Abstract

Background and objectives: The pathogenesis of chancroid is currently unclear. There are discrepancies between the virulence of Haemophilus ducreyi in the human and animal experiments. Iron availability influences the virulence of many pathogens. The objective of this study was to investigate the role of iron in virulence of H. ducreyi.

Study design: Intradermal inoculation of the primate Macaca mulatta was studied as an animal model for pathogenesis of chancroid. This model then was used to study the influence of iron availability on virulence of H. ducreyi. Eleven strains of H. ducreyi with proven avirulence in the rabbit intradermal test and one virulent control strain were used. Two of the strains had been shown to cause ulcers in a human inoculation experiment. Strains were suspended in fluid with different iron compounds before intradermal injection. Other monkeys were treated with injectable iron before inoculation with bacteria suspended.

Results: All but one of the test strains produced a chancroid-like ulcer from which H. ducreyi could be isolated. The minimal ulcerative dose was 10(5) cfu. Iron in the injection fluid decreased this dose 10-fold. In animals pretreated with intramuscular iron, the minimal ulcerative dose decreased to 10(4) cfu and all eleven strains became ulcerative.

Conclusions: The availability of iron increases virulence of H. ducreyi. The iron pretreated primate model is useful for the study of virulence factors of H. ducreyi because of its ability to produce lesions with strains that avirulent in other animal models but pathogenic to humans.