Seventeen strains of Haemophilus ducreyi were isolated from genital lesions which were negative for syphilis by dark-field examination. Media used for primary isolation at various times during the study were enriched chocolate agar, chocolate agar plus vancomycin (3 microgram/ml), rabbit blood agar plus vancomycin (3 micrograms/ml), fetal bovine serum agar, and fetal bovine serum agar plus vancomycin (3 micrograms/ml). H. ducreyi was isolated on chocolate agar plus vancomycin from 10 of 14 patients found to be positive on one or more media, on rabbit blood agar plus vancomycin from 16 of 17 patients, and on fetal bovine serum agar plus vancomycin from 9 of 11 patients. Sera from six animal species were tested to determine if any would support the growth of H. ducreyi. Horse and rabbit sera supported light growth of some strains. Fetal bovine serum supported good growth of all strains included in the study. Biochemical and physiological tests were done on the 17 isolates, a reference strain of H. ducreyi, and two reference strains of Haemophilus haemoglobinophilus. The results agreed with those reported by Kilian, except that H. ducreyi produced alpha-hemolysis in stabs on rabbit blood agar and was oxidase positive, three strains were urease positive, and CO2 improved the growth of seven strains. All 17 isolates were beta-lactamase positive. The reference strains were beta-lactamase negative.
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