EVALUATION OF AN ISOGENIC HEMOLYSIN-DEFICIENT MUTANT IN THE HUMAN-MODEL OF HAEMOPHILUS-DUCREYI INFECTION

Haemophilus ducreyi causes the genital ulcerative disease chancroid. O ne putative virulence factor of H. ducreyi is a pore-forming hemolysin that displays toxicity against human fibroblasts and keratinocytes, I n order to test the role of the hemolysin in pathogenesis, an isogenic hemolysin-deficient mutant was constructed, designated 35000HP-RSM1. The lipooligosaccharide, outer membrane protein patterns, and growth a ttributes of 35000HP-RSM1 were identical to its parent, 35000HP, Human subjects were challenged on the upper arm with the isogenic isolates in a double-blinded, randomized, escalating dose-response study, Pustu les developed at a similar rate at sites inoculated with the mutant or parent. The cellular infiltrate and bacterial load in lesions were al so similar. These results indicate the hemolysin does not play a role in pustule formation. Due to the limitations of this model, the role o f the hemolysin at later stages of infection could not be determined.