Characterization of skin lesions in mice following intradermal inoculation of Haemophilus ducreyi.

Twelve strains of H. ducreyi, which included two reference strains, were each inoculated intradermally into the flanks of CBA mice. All strains produced self-limited lesions which were macroscopically and microscopically typical of those seen in chancroid. Pustular nodules, about 5mm in diameter, developed at all inoculation sites by the second day when 10(7) organisms were inoculated. Approximately half of these lesions ulcerated and all had regressed by 2 weeks. Smaller nodules developed at about half the sites from the second to the fifth day when 10(6) or 10(5) organisms were given, but these did not ulcerate. No lesions were seen when 10(3) organisms were inoculated. Organisms were recovered from the lesions up to 11 days after inoculation. Specific H. ducreyi antigen, sought by a monoclonal antibody test, was detected in lesions up to 15 days following inoculation. Heat-killed organisms of H. ducreyi also produced nodules and ulcers although these were slightly smaller than those which developed after inoculation of viable bacteria. Similar lesions to those caused by H. ducreyi were produced after intradermal inoculation of about 10(8) viable or killed Neisseria gonorrhoeae organisms. Treatment of mice with ceftriaxone had little or no effect on the subsequent development of H. ducreyi-induced lesions. These findings indicated that the lesions were not produced specifically by viable H. ducreyi organisms. Ulcers were also produced following intradermal inoculation of purified lipopolysaccharide (LPS) from H. ducreyi or N. gonorrhoeae, but not by cell-free filtrates prepared from H. ducreyi cultures indicating a possible role for LPS in the pathogenesis of ulcerative skin lesions.