Typing Haemophilus ducreyi by indirect immunofluorescence assay.

Rabbits were inoculated with untreated whole cells of 16 strains of Haemophilus ducreyi. Homologous titres in an indirect immunofluorescence test ranged from 1/320 to 1/1280. No cross reactions, or very few, were observed between antisera to these strains and 22 other (possible taxonomically related) species, strains, and genera. A large diversity in types of antigen was observed among the strains of H ducreyi. Antiserum from two antigens (35000 and 3138), however, reacted with all 16 H ducreyi antigens tested. At least nine of the strains of H ducreyi examined could be identified as determining the type of antigen.

Antimicrobial susceptibility and characterization of outer membrane proteins of Haemophilus ducreyi isolated in Thailand.

One hundred strains of Haemophilus ducreyi isolated in Thailand from patients with chancroid were tested by the agar dilution method against 10 antimicrobial agents and typed by outer membrane protein pattern by using sodium dodecyl sulfate gel electrophoresis. All strains produced beta-lactamase and were resistant to tetracycline, kanamycin, and sulfonamides. Most had a decreased susceptibility to trimethoprim (MIC for 50% of the strains [MIC50], 0.5 micrograms/ml) and chloramphenicol (MIC50, 8 micrograms/ml). Strains were susceptible to ciprofloxacin (MIC90, 0.001 micrograms/ml), ceftriaxone (MIC50, 0.0015 micrograms/ml), erythromycin (MIC50, 0.015 micrograms/ml), rosoxacin (MIC50, 0.03 micrograms/ml), and spectinomycin (MIC50, 8 micrograms/ml). The degree of antimicrobial resistance found in Thailand is higher than that reported for H. ducreyi isolated in other regions. Five different outer membrane protein patterns were found by analyzing proteins in the range of 29 to 61 kilodaltons, but 98% of the Thai strains fell into three patterns which did not differ greatly. Outer membrane protein patterns of Thai strains were also seen in strains from other geographic areas. A new outer membrane protein type was found among nine strains isolated in Singapore.

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.