Characteristics of Haemophilus ducreyi in culture

Growth on different media and the influence of culture conditions were studied on 19 recently isolated strains of Haemophilus ducreyi, none of which had more than four passages on artificial media. The results were compared with 10 laboratory strains, which had an unknown number of passages in vitro. For all strains, growth was best on 30% rabbit blood agar and on Bieling agar. The laboratory strains showed a tendency to grow better on chocolate agar than did the fresh isolates. Of 19 fresh clinical isolates, 12 were CO2 dependent, and 2 needed extra moisture for growth. From the 10 laboratory strains, only one needed CO2 and none needed extra moisture. All 29 strains grew under anaerobic conditions. Of the 19 fresh clinical isolates, 12 grew at 22 degrees C, but only 2 of the 10 laboratory strains grew at this temperature. The laboratory strains grew better than the fresh isolates at 37 degrees C, and the optimal pH for all strains was pH 6.5 to 7.0. All strains showed starch aggregation.