Identification of Haemophilus ducreyi in the clinical laboratory

Some of the characteristics of 42 clinical isolates of Haemophilus ducreyi are reported. Only six of the 42 strains were able to grow on horse-blood agar. All strains gave a positive oxidase test with tetramethyl-p-phenylenediamine and a negative result with dimethyl-p-phenylenediamine. All of 15 test strains were negative in the porphyrin test. Tests for haemin requirement were inconclusive because of difficulties encountered in obtaining growth on a basal medium.