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The etiological agent of the sexually transmitted genital ulcer disease chancroid was first described in 1889 by Auguste Ducrey following repeated autoinoculation of purulent ulcer material from a series of patients. The organism was isolated on artificial media a decade later but has remained difficult to isolate consistently, resulting in controversy over its characteristics and role as the causative agent of chancroid. Because of its fastidious growth requirements, including unknown components in blood, the organism was included in the original description of the genus Haemophilus. Requirement for exogenous hemin and limited phenotypic characteristics, including structural and antigenic properties, suggested that Haemophilus ducreyi was a valid member of the genus Haemophilus. Recent studies of respiratory quinones, deoxyribonucleic acid hybridization, and competition for homologous transformation of the type species, H. influenzae, suggest that H. ducreyi is unrelated to any of the present species of the family Pasteurellaceae, which includes members of the genera Haemophilus, Actinobacillus, and Pasteurella. This review summarizes the early studies with H. ducreyi and our current knowledge of the microbiology of this important human pathogen.

The authors conducted a double-blind randomized clinical trial comparing single-dose cefotaxime (1 g im) plus daily placebo injections with cefotaxime (1 g im on each of three days). Each regimen was given with probenicid (1 g orally) for the treatment of chancroid. Twenty Haemophilus ducreyi culture-positive men received the single-dose cefotaxime regimen; in eight patients ulcers or buboes failed to respond to therapy. Nineteen H. ducreyi culture-positive men received cefotaxime on each of three days; H. ducreyi was eradicated from all patients, but one had a continuing ulcer and another had a bubo that failed to respond. Thus cefotaxime (1 g im daily for three days) plus probenicid (1 g orally) is effective therapy for chancroid. The lack of efficacy for chancroid of the single-dose cefotaxime regimen is surprising, given the remarkable susceptibility of H. ducreyi to cefotaxime; presumably the half-life of cefotaxime is too short for predictable eradication of H. ducreyi from the ulcer with a single-dose regimen.

Seventeen strains of Haemophilus ducreyi were isolated from genital lesions which were negative for syphilis by dark-field examination. Media used for primary isolation at various times during the study were enriched chocolate agar, chocolate agar plus vancomycin (3 microgram/ml), rabbit blood agar plus vancomycin (3 micrograms/ml), fetal bovine serum agar, and fetal bovine serum agar plus vancomycin (3 micrograms/ml). H. ducreyi was isolated on chocolate agar plus vancomycin from 10 of 14 patients found to be positive on one or more media, on rabbit blood agar plus vancomycin from 16 of 17 patients, and on fetal bovine serum agar plus vancomycin from 9 of 11 patients. Sera from six animal species were tested to determine if any would support the growth of H. ducreyi. Horse and rabbit sera supported light growth of some strains. Fetal bovine serum supported good growth of all strains included in the study. Biochemical and physiological tests were done on the 17 isolates, a reference strain of H. ducreyi, and two reference strains of Haemophilus haemoglobinophilus. The results agreed with those reported by Kilian, except that H. ducreyi produced alpha-hemolysis in stabs on rabbit blood agar and was oxidase positive, three strains were urease positive, and CO2 improved the growth of seven strains. All 17 isolates were beta-lactamase positive. The reference strains were beta-lactamase negative.