Haemophilus ducreyi are fastidious gram-negative coccobacilli bacteria.
This species causes the sexually transmitted disease chancroid, a major cause of genital ulceration in developing countries characterized by painful sores on the genitalia. The first study linking this disease with the agent Hemophilus ducreyi was published in 1889 by Auguste Ducrey. Each year in the United States, there are over 2,000 cases of chancroid.
H. ducreyi can be cultured on chocolate agar and incubated in an environment with elevated humidity and CO<sub>2</sub> enrichment at 33° to 35 °C. It is best treated with a macrolide, e.g. azithromycin, and a third-generation cephalosporin, e.g. ceftriaxone.
Morphology
Haemophilus ducreyi is a Gram-negative coccobacillus, and has a shape between a spherical coccus and a rod-shaped bacterium.
Colonies
Colonies of Haemophilus ducreyi are described as yellow-grey, small, and semiopaque as well as nonmucoid. Scanning electron microscopy has been used to observe that the microbe can form a colony of many cells; the cells adhere to each other because of an intercellular matrix. This bond can make it difficult to isolate a single cell of Haemophilus ducreyi, hindering the genetic studies that have been done on the microbe. A saturated atmosphere with elevated CO<sub>2</sub> levels is considered optimal for most strains, and the most favorable growth has been observed to occur under micro-aerophilic conditions achieved in a sealed anaerobic jar without a catalyst, using two envelopes that generate CO<sub>2</sub> and H<sub>2</sub>, commonly referred to as Campylobacter growth conditions.
Toxins
Haemophilus ducreyi is able to defend itself against the immune response's T cells through two toxins: a hemolysin and the cytolethal distending toxin (CDT). CDT is characterized by its ability to arrest epithelial cells in the G2 phase of the cell cycle and combats T cells by inducing apoptosis. Together, these toxins showcase the adeptness of H. ducreyi in manipulating host cell processes.
Diagnosis
Although antigen detection, serology, and genetic amplification methods are sometimes used to diagnose infections with H. ducreyi and the genetic tests have greater sensitivity, they are not widely available, so cultures are currently considered the "gold standard" test, which has about 80% sensitivity under optimal combination of media.
Treatment
Single-dose antibiotic treatments using macrolides, third-generation cephalosporins, or fluoroquinolone continue to be effective in treating chancroid. The first line treatments recommended by the U.S. Centers for Disease Control and Prevention are one of four options: azithromycin one gram orally in a single dose, ceftriaxone 250 mg intramuscularly in a single dose, ciprofloxacin 500 mg orally two times a day for three days, or erythromycin base 500 mg orally three times a day for seven days. Some antibodies were specific to all strains, while others targeted only certain groups of strains H. ducreyi, indicating that the outer membrane proteins of H. ducreyi can vary in their immune recognition.