Ascorbic Acid Uptake and Utilization Encoded by ulaABCD Is Dispensable for the Virulence of Haemophilus ducreyi in Humans.

Compared to wounded skin, ascorbic acid is enriched in pustules of humans experimentally infected with Haemophilus ducreyi. Compared to the broth grown inocula, transcription of the H. ducreyi ulaABCD operon, which encodes genes for ascorbic acid uptake, is increased in pustules. We hypothesized that ascorbic acid uptake plays a role in H. ducreyi virulence. Five volunteers were infected with both H. ducreyi strain 35000HP and its isogenic ulaABCD deletion mutant at multiple sites; the papule and pustule formation rates of the mutant and parent strains were similar. Thus, ascorbic acid uptake is not essential for H. ducreyi virulence in humans.