Pustule Formation Rates Research Articles

Cumulative Experience with Haemophilus ducreyi 35000 in the Human Model of Experimental Infection

To study Haemophilus ducreyi pathogenesis, the authors developed an experimental model of infection in human volunteers. The authors analyze their cumulative experience with strain 35000 in the model and calculate the papule and pustule formation rates for estimated delivered doses (EDDs) ranging from 1 cfu to 100 cfu. Sixty-five volunteers were included in the analysis. A total of 139 sites were available for calculation of the papule formation rate, and 117 sites were available for calculation of the pustule formation rates. The effect of EDDs and probabilities of papule formation and the pustule formation were dose-dependent. Increasing the EDD resulted in a higher probability of papule and pustule formation. H ducreyi is highly infectious for humans. Inoculation of an EDD of 1 cfu causes a papule formation rate of 50%. Pustule formation rates are approximately 50% for 27 cfu and 90% for 100 cfu.

Expression of sialylated or paragloboside-like lipooligosaccharides are not required for pustule formation by Haemophilus ducreyi in human volunteers.

The lipooligosaccharide (LOS) of Haemophilus ducreyi, the etiologic agent of chancroid, chemically and immunologically resembles human glycosphingolipid antigens. To test whether LOS that contains paragloboside-like structures was required for pustule formation, an isogenic mutant (35000HP-RSM2) was constructed in losB, which encodes D-glycero-D-manno-heptosyltransferase. 35000HP-RSM2 produces a truncated LOS whose major glycoform terminates in a single glucose attached to a heptose trisaccharide core and 2-keto-3-deoxyoctulosonic acid. Five human subjects were inoculated with 35000HP and 35000HP-RSM2 in a dose-response trial. For estimated delivered doses (EDDs) of >/=25 CFU, the pustule formation rates were 80% for 35000HP and 58% for 35000HP-RSM2. Preliminary data indicated that a previously described Tn916 losB mutant made a minor glycoform that does not require DD-heptose to form the terminal N-acetyllactosamine. If 35000HP-RSM2 made this glycoform, then 35000HP-RSM2 could theoretically make a sialylated glycoform. To test whether sialylated LOS was required for pustule formation, a second trial comparing an isogenic sialyltransferase mutant (35000HP-RSM203) to 35000HP was performed in five additional subjects. For EDDs of >/=25 CFU, the pustule formation rates were 30% for both 35000HP and 35000HP-RSM203. The histopathology and recovery rates of H. ducreyi from surface cultures and biopsies obtained from mutant and parent sites in both trials were similar. These results indicate that neither the expression of a major glycoform resembling paragloboside nor sialylated LOS is required for pustule formation by H. ducreyi in humans.