ANTIGEN-DETECTION AND IMMUNOLOGICAL TYPING OF HAEMOPHILUS-DUCREYI WITH A SPECIFIC RABBIT POLYCLONAL SERUM

A rabbit polyclonal serum was raised against the 29-kDa species-specif ic marker, as well as the 30- to 34-kDa immunotype-specific markers of Haemophilus ducreyi described elsewhere (E. Roggen, S. De Breucker, E . Van Dyck, and P. Piot, Infect. Immun. 60:590-595, 1992). These antig ens were purified from a cocktail of H. ducreyi isolates by sodium dod ecyl sulfate-polyacrylamide gel electrophoresis. The immune serum reac ted in enzyme-linked immunosorbent assay (ELISA) preferentially with H . ducreyi, at a titer as high as 50,000. To make it specific to H. duc reyi, nonspecific antibodies were removed by adsorption on a mixture o f Haemophilus spp., Escherichia coli, Candida albicans, and Corynebact erium spp. In the 29- to 34-kDa region of immunoblot profiles from H. ducreyi isolates (n = 450), the adsorbed serum revealed essentially th e same antigens as did a pool of well-characterized human sera. Yet, e ight different immunotypes were observed. With this rabbit polyclonal serum, an ELISA-based antigen detection test was developed. The adsorb ed serum reacted specifically with all H. ducreyi isolates tested (n = 450), but not with other bacterial species (n = 15). This test was ev aluated with a limited number of clinical specimens from African patie nts with culture-proven chancroid and no evidence for any other ulcera ting etiology (n = 10) and a number of chancroid-negative control pati ents from Belgium (n = 20). Within this context, the test yielded a se nsitivity and specificity of 100%.