Monoclonal antibodies reactive with all strains of Haemophilus ducreyi

Localization of Haemophilus ducreyi at the pustular stage of disease in the human model of infection

To localize Haemophilus ducreyi in vivo, human subjects were experimentally infected with H. ducreyi until they developed a painful pustule or for 14 days. Lesions were biopsied, and biopsy samples were fixed in 4% paraformaldehyde, and cryosectioned. Sections were stained with polyclonal anti-H. ducreyi antiserum or H. ducreyi-specific monoclonal antibodies (MAbs) and fluorescently tagged secondary antibodies and examined by confocal microscopy. We identified H. ducreyi in 16 of 18 pustules but did not detect bacteria in the one papule examined. H. ducreyi was observed as individual cells and in clumps or chains. Staining with MAbs 2D8, 5C9, 3B9, 2C7, and 9D12 demonstrated that H. ducreyi expresses the major pilus subunit, FtpA, the 28-kDa outer membrane protein Hlp, the 18-kDa outer membrane protein PAL, and the major outer membrane protein (MOMP) or OmpA2 in vivo. By dual staining with polyclonal anti-H. ducreyi antiserum and MAbs that recognize human skin components, we observed bacteria within the neutrophilic infiltrates of all positively staining pustules and in the dermis of 10 of 16 pustules. We were unable to detect bacteria associated with keratinocytes in the samples examined. The data suggest that H. ducreyi is found primarily in association with neutrophils and in the dermis at the pustular stage of disease in the human model of infection.

The major outer membrane protein of Haemophilus ducreyi consists of two OmpA homologs

The major outer membrane protein (MOMP) of Haemophilus ducreyi is an OmpA homolog that migrates on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) gels as three species with apparent molecular weights ranging from 37,000 to 43,000. Monoclonal antibodies directed against this macromolecule were used to identify recombinant clones containing fragments of the gene encoding this protein. Nucleotide sequence analysis of these fragments confirmed that the MOMP encoded by the intact gene (momp) was a member of the OmpA family of outer membrane proteins. Construction of an isogenic H. ducreyi mutant unable to express the MOMP led to the discovery of a second outer membrane protein which migrated at the same rate on SDS-PAGE gels as the MOMP. N-terminal amino acid sequence analysis of this second protein revealed that its N terminus was nearly identical to that of the MOMP and also had homology with members of the OmpA family. Nucleotide sequence analysis of the region downstream from the momp gene revealed the presence of a partial open reading frame encoding a predicted OmpA-like protein. A modification of anchored PCR technology was used to obtain the nucleotide sequence of this downstream gene which was shown to encode a second OmpA homolog (OmpA2). The N-terminal amino acid sequence of OmpA2 was identical to that of the OmpA-like protein detected in the momp mutant. The H. ducreyi MOMP and OmpA2 proteins, which comigrated on SDS-PAGE gels and which were encoded by the tandem arranged momp and ompA2 genes, were 72% identical.

A morphological study of penile chancroid lesions in human immunodeficiency virus (HIV)-positive and -negative African men with a hypothesis concerning the role of chancroid in HIV transmission

Chancroid, the most common cause of genital ulceration in Africa, is known to be associated epidemiologically with heterosexual transmission of human immunodeficiency virus (HIV). The pathophysiological mechanisms by which chancroid might facilitate the spread of HIV are obscure. To investigate the role of chancroid in HIV transmission, the authors studied the histological features of biopsies from 11 men with penile chancroid lesions including five who were serologically positive for HIV. The histomorphologic and immunophenotypic nature of the inflammatory infiltrates suggests that there is a significant role for cell-mediated immunity in the host response to Hemophilus ducreyi infection. This response may be critical to the role of chancroid in HIV transmission.

Monoclonal antibodies against Haemophilus ducreyi lipooligosaccharide and their diagnostic usefulness

Monoclonal antibodies against the lipooligosaccharide of Haemophilus ducreyi were produced. Two of them, MAHD6 and MAHD7, were found to be relatively, although not absolutely, specific and reacted with nearly all strains of Haemophilus ducreyi tested: 59 of 60 and 60 of 60, respectively. The diagnostic usefulness of MAHD7 was assessed. Clinical specimens collected in Zambia from patients with genital ulcers were tested using indirect immunofluorescence (IF), enzyme immunoassay (EIA), the polymerase chain reaction (PCR) and bacterial culture. Compared with culture, IF had a sensitivity of 100%; compared with PCR, sensitivity was 89%. The corresponding figures for the EIA were 83% and 74%, respectively. The sensitivity of culture compared with PCR was 63%. The results suggest that IF on genital smears using MAHD7 might be an excellent tool for the diagnosis of chancroid in high-prevalence populations. However, further evaluation of the specificity of this test is needed.

Detection of Haemophilus ducreyi lipooligosaccharide by means of an immunolimulus assay

A murine monoclonal antibody (MAb) directed against a surface-exposed epitope of the lipooligosaccharide (LOS) of Haemophilus ducreyi strain 35000 was shown to be reactive with all 37 strains of this pathogen tested in a colony blot-radioimmunoassay. The LOS epitope bound by this MAb appeared to be stably expressed by H. ducreyi growing in vitro. The use of this MAb in the immunolimulus system revealed that it could detect purified H. ducreyi LOS at a level of 25 pg/ml. Similarly, this immunolimulus system could detect as few as 1000 colony forming units of in vitro-grown H. ducreyi cells per ml of buffer. When this MAb was utilized in the immunolimulus system together with lesion material from rabbits infected with two different H. ducreyi strains, a positive reaction was obtained with every sample tested, even when no viable organisms were present in the lesion material. In contrast, this MAb yielded consistently negative results when used in the immunolimulus system with lesion material from animals infected with Staphylococcus aureus.

Chancroid and Haemophilus ducreyi: an update

Haemophilus ducreyi is a fastidious gram-negative bacillus that causes the sexually transmitted infection chancroid. Chancroid is a major genital ulcerative disease in Africa, Southeast Asia, the Caribbean, and Latin America and is of increasing concern in the United States. Genital ulcerative disease and chancroid in particular have been associated with facilitating the transmission of human immunodeficiency virus. The diagnosis of chancroid based on the clinical appearance of the genital lesion or on the isolation of H. ducreyi on selective medium is relatively insensitive. However, recent advances in nonculture diagnostic tests have enhanced our ability to diagnose chancroid. There has been renewed interest in understanding the pathogenesis of H. ducreyi. In vitro and in vivo models have been developed to help identify important virulence determinants. Through the use of biochemical and molecular techniques, macromolecular components that may be important in virulence have been identified.

Haemophilus ducreyi

Genital ulcer disease as a risk factor for HIV transmission has become apparent in the fight against AIDS. In poor communities in developing countries with people living under low hygienic conditions chancroid is often reported to be the most common form of genital ulcer. It is caused by Haemophilus ducreyi; a fastidious bacterium, notoriously difficult to grow in the laboratory. Apart from a few small micro-epidemics from time to time the disease, which has interesting immunological aspects, is now rare and almost forgotten in most industrialized countries. This may be part of the reason why there is no simple and inexpensive diagnostic test available yet that would be useful in the low-resource settings where chancroid is prevalent. The present review focuses on the diagnosis and pathogenesis of chancroid.

Evidence for a common epitope on the surface of Mycoplasma gallisepticum defined by monoclonal antibody

An antigen containing a common epitope in most strains of Mycoplasma gallisepticum was purified by isoelectric focusing and used in the production of monoclonal antibodies (mAb). Of several mAb produced, only one mAb reacted with focused component and with all six strains of M. gallisepticum except strain 6/85. This mAb was designated MG3D6.A5, and it was subsequently purified with immobilized rProtein Atm. The MG3D6.A5 mAb recognized a common epitope on a molecule with relative molecular weight of 98 kilodaltons (kDa), termed p98. No binding was observed when the MG3D6.A5 mAb was reacted against antigens extracted from other mycoplasma species, indicating its species-specificity. Physicochemical studies revealed that p98 had an isoelectric point of 5.2, was stable to heat, and was resistant to periodate oxidation but sensitive to trypsin treatment, suggesting that p98 is a nonglycosylated protein. Furthermore, ultrastructural studies with colloidal gold revealed that M. gallisepticum cells were selectively stained with MG3D6.A5 mAb to p98. The latter was focally distributed on the surface of a mycoplasma cell membrane near the attachment organelle. These results suggest that p98 is a highly conserved protein in M. gallisepticum strains, is immunogenic, and is surface-accessible; its binding specificity to MG3D6.A5 mAb could be used to identify M. gallisepticum in multiple cultures.

The major outer membrane protein of Haemophilus ducreyi is a member of the OmpA family of proteins

Haemophilus ducreyi contains a major outer membrane protein (MOMP) whose apparent molecular weight is 39,000 to 42,000 for all strains tested. Two monoclonal antibodies (MAbs), designated 9D12 and 2C7, bound to the MOMP for all strains of H. ducreyi tested. As reported previously, MAb 9D12 was H. ducreyi specific (E. J. Hansen and T. A. Loftus, Infect. Immun. 44:196-198, 1984). MAb 2C7 bound to all members of the family Pasteurellaceae tested, suggesting that the MAbs bound to distinct epitopes on the MOMP. The MOMP was purified by extraction of whole cells with Zwittergent and ion-exchange chromatography. A peak eluted from a cation-exchange column contained three bands. All three species bound both MAbs, and the fraction yielded a single N-terminal amino acid sequence, suggesting that the bands represented different conformations of the MOMP. The MOMP was heat modifiable, contained two cysteine residues, and was cationic at pH 8.0, features not usually associated with classical porin proteins. The N-terminal amino acid sequence and total amino acid content of the MOMP were homologous to the OmpA proteins of members of the family Enterobacteriaceae and the OmpA-like protein of Actinobacillus actinomycetemcomitans. An OmpA-specific polyclonal serum bound to the MOMP, and MAb 2C7 bound to Haemophilus influenzae protein 5, an OmpA-like protein, indicating that the MOMP was antigenically related to OmpA. These data indicated that the most abundant protein in the outer membrane of H. ducreyi was not a classical porin and belonged to the OmpA family of proteins.

Development of the polymerase chain reaction for diagnosis of chancroid

The published nucleotide sequences of the 16S rRNA gene of Haemophilus ducreyi were used to develop primer sets and probes for the diagnosis of chancroid by polymerase chain reaction (PCR) DNA amplification. One set of broad specificity primers yielded a 303-bp PCR product from all bacteria tested. Two 16-base probes internal to this sequence were species specific for H. ducreyi when tested with 12 species of the families Pasteurellaceae and Enterobacteriaceae. The two probes in combination with the broad specificity primers were 100% sensitive with 51 strains of H. ducreyi isolated from six continents over a 15-year period. The direct detection of H. ducreyi from 100 clinical specimens by PCR showed a sensitivity of 83 to 98% and a specificity of 51 to 67%, depending on the number of amplification cycles.

Standardization of an enzyme immunoassay for human antibody to Haemophilus ducreyi

We standardized a serologic enzyme immunoassay (EIA) for human immunoglobulin G and M antibodies against Haemophilus ducreyi. We evaluated the performance of this test with respect to the time from acute chancroid and coinfection with human immunodeficiency virus (HIV). Antibody to a crude, soluble bacterial antigen of one H. ducreyi strain was detected in a panel of serum samples from clinically and microbiologically confirmed cases of chancroid and from controls. Test interpretation was standardized for optimal sensitivity and specificity. Performance of the EIA was enhanced in the period of early convalescence from acute primary chancroid and was not diminished in the presence of HIV coinfection. The EIA performed adequately as a serologic screening test for field evaluation and epidemiologic application in conjunction with sexually transmitted disease and HIV detection and control efforts.

Use of electroporation to construct isogenic mutants of Haemophilus ducreyi

Little is known about the genetics of Haemophilus ducreyi, the etiologic agent of chancroid. To develop a method for constructing isogenic mutants of this organism that could be utilized in pathogenesis-related studies, electroporation techniques were evaluated as a means of introducing DNA into this organism. Electroporation of the plasmid shuttle vector pLS88 into H. ducreyi yielded approximately 10(6) antibiotic-resistant transformants per microgram of plasmid DNA. Studies of the feasibility of moving mutated genes into H. ducreyi were initiated by using NotI linker insertion and mini-Tn10kan mutagenesis techniques to introduce insertion mutations into cloned H. ducreyi genes encoding cell envelope antigens. In the former case, a gene encoding chloramphenicol acetyltransferase was then inserted into the NotI linker site created in the cloned H. ducreyi gene. The recombinant Escherichia coli strains containing these mutated plasmids no longer expressed the homologous H. ducreyi cell envelope antigens, as evidenced by their lack of reactivity with monoclonal antibody probes for these H. ducreyi proteins. Subsequent electroporation of both circular and linearized forms of plasmids carrying these mutated H. ducreyi genes into the homologous wild-type strain of H. ducreyi yielded antibiotic-resistant transformants which also lacked reactivity with the cell envelope antigen-specific monoclonal antibodies. Southern blot analysis confirmed that homologous recombination had occurred in these monoclonal antibody-unreactive transformants, resulting in the replacement of the wild-type allele with the mutated allele. Allelic exchange was most efficient when linear DNA molecules were used for electroporation. These results indicate that electroporation methods can be utilized to construct isogenic mutants of H. ducreyi.

Characterization of an 18,000-molecular-weight outer membrane protein of Haemophilus ducreyi that contains a conserved surface-exposed epitope

Identification of antigenically conserved surface components of Haemophilus ducreyi may facilitate the development of reagents to diagnose and prevent chancroid. A hybridoma derived from a mouse immunized with nontypeable Haemophilus influenzae produced a monoclonal antibody (MAb), designated 3B9, that bound to 35 of 35 H. ducreyi strains isolated from diverse geographic regions. The MAb 3B9 bound to a non-heat-modifiable H. ducreyi outer membrane protein (OMP) whose apparent molecular weight was 18,000 (the 18K OMP), and the 3B9 epitope did not phase vary at a rate of greater than 10(-3) in H. ducreyi. In immunoelectron microscopy, the 3B9 epitope was surface exposed, and there was intrastrain and interstrain variability in the amount of 3B9 labelling of whole cells. The MAb 3B9 cross-reacted with many species of the family Pasteurellaceae and bound to the 16.6K peptidoglycan-associated lipoprotein (P6 or PAL) of H. influenzae. Unlike P6, the 18K OMP did not copurify with peptidoglycan. In Western blots (immunoblots), five of seven serum samples obtained from patients with chancroid and four of five serum samples obtained from patients with other genital ulcer diseases at the time of presentation contained antibodies that bound to the 18K OMP. In a competition enzyme-linked immunosorbent assay, four of these serum samples inhibited the binding of 3B9 to H. ducreyi by more than 50%. We conclude that members of Pasteurellaceae expressed a conserved epitope on OMPs that sometimes had different physical characteristics. Patients with chancroid usually have antibodies to the 18K OMP and the 3B9 epitope that may have resulted from infection with H. ducreyi or previous exposure to other Haemophilus or Actinobacillus sp. strains.

Sexually transmitted diseases: bacterial infections. Committee on Sexually Transmitted Diseases of the American Academy of Dermatology

This update reviews the latest diagnostic and therapeutic methods regarding sexually transmitted diseases caused by bacteria. The following mucocutaneous bacterial disorders will be discussed: syphilis, chancroid, lymphogranuloma venereum, granuloma inguinale, and gonorrhea.

Biology of Haemophilus ducreyi

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.

Rapid detection of Haemophilus ducreyi in clinical and experimental infections using monoclonal antibody: a preliminary evaluation

A monoclonal antibody raised against Haemophilus ducreyi was tested for its sensitivity and specificity as an immunofluorescence (IF) reagent using simulated vaginal smears containing H. ducreyi, smears taken from skin lesions of mice infected with H. ducreyi and patients from South Africa, Thailand and Malaysia with clinically diagnosed chancroid. The IF test was more sensitive than culture or Gram staining in the simulated smears, theoretically detecting less than 4 organisms/sample. It detected H. ducreyi in 95% of the animal lesions compared with 14% detected by culture. Immunofluorescence testing identified over 90% of culture-positive cases of chancroid but also detected organisms in some culture-negative cases where clinical evidence for the diagnosis was strong. These results suggest that this antibody may provide a simple, rapid and sensitive means of detecting H. ducreyi in cases of chancroid.

Production of monoclonal antibodies specific for Haemophilus ducreyi: a screening method to discriminate specific and cross-reacting antibodies

Haemophilus ducreyi is the etiological agent of chancroid. The organism shares extensive immunological cross-reactivity with other Haemophilus species. This presents substantial difficulties for the production of specific monoclonal antibodies (MAbs). A competition ELISA was devised for hybridoma screening which allowed the detection of H. ducreyi-specific antibody-producing hybridoma cultures during the initial screening process. With this screening method, seven MAbs specific for H. ducreyi were obtained in a single cell fusion exercise. The specificities of the 7 MAbs were demonstrated by direct ELISA and dot immunobinding assays against several strains each of H. influenzae, H. parainfluenzae and Neisseria gonorrhoeae. Five of the MAbs reacted against all ten strains of H. ducreyi. These MAbs may permit the development of rapid and efficient immunodiagnostics for chancroid. The principle of the competition ELISA for hybridoma screening should be widely applicable to the development of specific MAbs to other organisms in which immunological cross-reactivity is an impediment to hybridoma screening by conventional methods.

Chancroid and Haemophilus ducreyi

Haemophilus ducreyi is the causative agent of chancroid, one of the genital ulcerative diseases. H. ducreyi is the major cause of genital ulcer disease in Africa and Southeast Asia and is of increasing concern in the United States. Definitive diagnosis of chancroid requires the isolation and identification of H. ducreyi, but isolation of this organism is difficult and the available medium is not optimal for all strains. Fluorescent antibody and serologic tests are of limited value. In general, our knowledge of this organism is rather limited, and indeed, recent studies have questioned the placement of H. ducreyi in the genus Haemophilus. H. ducreyi has relatively few biochemical activities, and epidemiologic studies are limited because there are limited phenotypic markers available for strain typing. Specific virulence factors of H. ducreyi have yet to be identified. Antimicrobial resistance in H. ducreyi is of special concern, as this organism has acquired both gram-negative and gram-positive resistance determinants. In addition, some of these determinants can be mobilized and transferred to other Haemophilus species or to Neisseria gonorrhoeae.

Immunoblot analysis of antigens associated with Haemophilus ducreyi using serum from immunised rabbits

Sodium dodecyl sulphate polyacrylamide gel electrophoresis and immunoblotting were used to characterise isolates of Haemophilus ducreyi. Isolates of H ducreyi were heterogeneous in protein composition, but isolates from single outbreaks appeared similar both in protein profiles and antigenic analysis. Rabbits immunised with H ducreyi responded with a vigorous humoral immune response in which multiple antigenic polypeptides were detected. The most prominent antigens had molecular masses of 67, 42, 22.5, and 20 kilodaltons.