Characteristics of Haemophilus ducreyi. A study

Enhanced recovery of Haemophilus ducreyi from clinical specimens by incubation at 33 versus 35 degrees C

Isolation rates of Haemophilus ducreyi from cases of chancroid are low. Experts recommend that isolation media be incubated at 33 to 35 degrees C, but the possible effect of this temperature range on the recovery of H. ducreyi has not been evaluated. We inoculated two sets of agar plates with material from genital ulcers and incubated one set at 33 degrees C and one at 35 degrees C; incubation at 33 degrees C identified 21% more cases than did incubation at 35 degrees C (109 versus 85 cases, respectively, of the 116 cases from which an isolation was made; P < 0.01).

Use of the RapID-ANA system and sodium polyanetholesulfonate disk susceptibility testing in identifying Haemophilus ducreyi

Haemophilus ducreyi has traditionally been difficult to identify. We have utilized simple test methods to identify 19 fresh isolates obtained during a recent outbreak of chancroid in Houston and six strains of H. ducreyi from other outbreaks. Tests were performed from growth on chocolate agar after 48 h of incubation at 35 degrees C with increased humidity and CO2. All isolates exhibited typical colonial morphology and Gram stain. Isolates were catalase negative and oxidase and nitrate positive (in enriched broth). The RapID NH system failed to identify these strains because of negative reactions with alkaline phosphatase and nitrate reductase. However, by using the RapID-ANA system, all strains were positive for alkaline phosphatase and arginine, glycine, and serine aminopeptidases. Their biochemical profiles were distinct from those obtained with 66 strains representing 13 species similar to H. ducreyi. We also investigated the use of sodium polyanetholesulfonate (SPS) disk susceptibility to identify and differentiate H. ducreyi from other species. All H. ducreyi isolates were susceptible, as evidenced by the presence of a zone of inhibition with an average size of 15 mm around the SPS disk. With the exceptions of Neisseria gonorrhoeae, Gardnerella vaginalis, and Capnocytophaga spp., no other strain showed any evidence of inhibition. The latter three organisms can be easily differentiated from H. ducreyi by various features including reactions in the RapID-ANA. We conclude that, by considering simple growth and biochemical characteristics, SPS susceptibilities, and reactions in RapID-ANA, it is possible for more clinical laboratories to definitively identify this organism.

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.

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.

Susceptibility of Haemophilus ducreyi to spectinomycin in vitro

Using an agar dilution technique with standardised inocula prepared by ultrasonication, the minimum inhibitory concentrations (MICs) of spectinomycin were determined for 66 strains of Haemophilus ducreyi, eight of which were beta lactamase producers. All strains were sensitive to concentrations of spectinomycin, which were well within the therapeutic ranges attained with normal dosage. The MIC50 and MIC90 were 8 mg/l, (range 0.007-16 mg/l).

Monoclonal antibodies reactive with all strains of Haemophilus ducreyi

We have isolated plasma cell hybridomas which secrete monoclonal antibodies directed against Haemophilus ducreyi. Two of these monoclonal antibodies recognize all strains of H. ducreyi tested to date and are capable of detecting the presence of H. ducreyi in skin lesions produced by this pathogen in experimental animals. These monoclonal antibodies which react with apparently all strains of H. ducreyi have the potential to be developed into a rapid immunodiagnostic test for chancroid.

Susceptibility of 40 Haemophilus ducreyi strains to 34 antimicrobial products

A study was performed to examine compounds that might improve the selectivity of the primary isolation medium for Haemophilus ducreyi. The susceptibility of 40 H. ducreyi strains to 34 antimicrobial agents, including 10 antibiotics, 3 quaternary ammonium compounds, 3 phenolic derivatives, 3 acridines, and 15 heavy metal compounds, was investigated by using an agar plate dilution technique. Results were compared with the susceptibilities of other gram-negative rods which may be contaminants on isolation media. The minimal inhibitory concentration range for colistin (16 to 128 micrograms/ml) indicated that this antibiotic might be of use as a selective agent. H. ducreyi was susceptible to spectinomycin (minimal inhibitory concentration range, 16 to 64 micrograms/ml), thiamphenicol (0.12 to 1 microgram/ml), chloramphenicol (0.12 to 0.5 micrograms/ml), and streptomycin (4 to 32 micrograms/ml) and moderately susceptible to kanamycin (2 to 8 micrograms/ml). For the heavy metal compounds, a high susceptibility was seen with copper(II) chloride (2 to 8 micrograms/ml, corresponding to a concentration of 0.75 to 3 micrograms of Cu2+ ions per ml), sodium selenite (1 to 4 micrograms/ml, or 0.45 to 1.83 micrograms of Se- ions per ml), and phenylmercury acetate (0.12 to 0.5 micrograms/ml). The minimal inhibitory concentrations of quaternary ammonium compounds, acridines, and phenolic derivatives were between 1 and 32 micrograms/ml, 8 and 32 micrograms/ml, and 8 and 250 micrograms/ml, respectively.

Oropharyngeal Haemophilus ducreyi infection

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