CHARACTERIZATION OF THE HEMOLYTIC-ACTIVITY OF HAEMOPHILUS-DUCREYI

H. ducreyi is the causative agent of chancroid, a genital ulcer diseas e most prevalent in developing countries. Chancroid enhances the heter osexual transmission of human immunodeficiency virus and is identified in focal outbreaks in the United States, but little is known about it s pathogenesis. We studied the hemolysin produced by H. ducreyi becaus e this molecule might be an important virulence factor in the pathogen esis of chancroid. Ten strains of H. ducreyi were tested on newly devi sed blood agar plates and were found to have hemolytic activity, We ex amined the hemolytic activity of H. ducreyi 35000 further and found th at it was heat labile, cell associated, greatest at pH 7.0, and produc ed in logarithmic- but not stationary-phase cultures. Using transposon s Tn916 and Tn1545-Delta 3, we have isolated three classes of transpos on mutants of strain 35000: those with no detectable hemolytic activit y, those with reduced hemolytic activity, and those with enhanced hemo lytic activity. Transposon insertions in the nonhemolytic mutants were located in a DNA sequence which hybridized to the Proteus mirabilis h emolysin gene, Analysis of clones containing overlapping sections of t his region served to further localize the H. ducreyi hemolysin gene an d allow its expression in Escherichia coli and complementation of the nonhemolytic defect in an H. ducreyi mutant. These experiments indicat e that H. ducreyi 35000 produces a hemolysin that is related to the ca lcium-independent hemolysin produced by P. mirabilis. Further experime nts are needed to define the similarity of the H. ducreyi hemolysin to other calcium-independent hemolysins and to determine its role in the pathogenesis of chancroid.