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.