Haemophilus ducreyi (Chancroid)

Haemophilus ducreyi is a Gram-negative coccobacillus, which means that shape-wise, it’s somewhere between a spherical coccus and a rod-like bacillus.

Haemophilus ducreyi is an obligate human pathogen and causes a sexually transmitted disease, called chancroid.Now, Haemophilus ducreyi has a thin peptidoglycan layer, so it doesn’t retain the crystal violet dye used during Gram staining.

Instead, like any other Gram-negative bacteria, it stains pink with safranin dye. So, under the microscope, the bacteria look like short or relatively long pink rods with rounded ends, that usually grow in chains, so they’re sometimes compared to a “school of fish”.Now, Haemophilus ducreyi is: non-motile, so it doesn’t move / facultatively anaerobic, which means it can survive in both aerobic and anaerobic environments / oxidase positive which means it produces an enzyme called oxidase / and catalase negative, which means it doesn’t produce an enzyme called catalase.Finally, Haemophilus ducreyi can be cultivated on chocolate agar, because this medium contains essential nutrients that Haemophilus ducreyi need to grow, like factor X, also called hemin.

They’re fastidious bacteria that only grow in a CO2 environment, at a temperature between 33 and 35 degrees Celsius, and it forms small, grey or translucent colonies.Now, Haemophilus ducreyi enters the body through mucosal and skin breaks and has a number of virulence factors, that are like assault weaponry that help it attack and destroy the host cells, and evade the immune system.Now, Haemophilus ducreyi is encapsulated, so it has a polysaccharide layer called a capsule, that acts like a shield, protecting the bacteria against phagocytic cells like macrophages and neutrophils.

On the capsule there are fimbria-like proteins, such as Flp1, Flp2 and Flp3 and uses them to attach to subcutaneous epithelial cells and fibroblasts.

Underneath the capsule there’s an outer membrane which consist of lipo-oligo-saccharide, or LOS, which is also involved in cell adhesion.

After attachment, Haemophilus ducreyi makes epithelial cells secrete proinflammatory cytokines like IL-6 and IL-8. These molecules signal for white blood cell reinforcements - specifically, IL-6 makes CD4 T-cells accumulate in the epidermis and dermis, while IL-8 leads to accumulation of poly-morpho-nuclear leukocytes and macrophages.

Now, neutrophils and macrophages try to kill invading bacteria by generating a bunch of toxic oxygen radicals, such as superoxide, which results from oxidative metabolic burst.

Unfortunately, Haemophilus ducreyi produces an enzyme called copper-zinc superoxide dismutase, which converts superoxide radicals to oxygen and hydrogen peroxide, so it survives the attack.

Furthermore, Haemophilus ducreyi makes two toxins. One of them, called cyto-lethal distending toxin, or HdCTD, causes G2/M cell cycle arrest, which means that it stops the cell cycle right when the cell is at its largest, in preparation for mitosis, or cell division.

So basically, the cell can’t divide to restore its normal size. Eventually, this causes cell death.

The other one is a cytotoxic hemolysin, which can lyse foreskin epithelial cells and immune system cells such as macrophages, T cells and B cells.

So, this leads to tissue destruction and avoidance of immune system.Finally, Haemophilus ducreyi needs zinc to thrive and replicate, so it has a zinc-binding protein that snatches zinc from the host cells.So, all of these processes lead to injury of epithelial cells and fibroblasts, which lead to disorganization of the epidermis and formation of erythematous papules; which are red elevations of the skin.

Eventually, papules collect pus and become pustules. Then, the pustules rupture, leaving behind an extremely painful ulcer with soft irregular margins, called a soft chancre.Now, Haemophilus ducreyi causes a disease called chancroid, which is a sexually transmitted disease.

Risk factors include multiple sex partners or unprotected sexual intercourse. Also, people with chancroid have a higher risk of acquiring or transmitting HIV infection.Now, the hallmark symptom of the disease is the soft chancre.

Multiple ulcers may be noted, as well as a result of multiple areas of microtrauma or as a result of direct contact between two adjacent areas resulting in “kissing ulcers”.

The base of the ulcer is covered with a gray or yellow purulent exudate and bleeds easily when scraped. Common sites of infection in men are: the pre-puce, corona, or the glans of the penis and in women are: the labia, vaginal introitus and perianal areas.

In women, symptoms may also include dysuria, which is pain during urination, dyspareunia, which is pain during sexual intercourse, abnormal vaginal discharge, rectal bleeding or painful defecation.

In 50% of cases, there may be painful inguinal lymphadenopathy, usually unilateral, which may become suppurative.Chancroid is usually diagnosed based on clinical findings such as one or more painful genital ulcers with tender suppurative inguinal adenopathy, after ruling out other genital ulcerative diseases, such as syphilis or herpes simplex virus infection.

Haemophilus ducreyi can also be isolated from an ulcer or lymph node aspirate, and grown in culture, but this is not commonly done in practice.

FInally, Haemophilus ducreyi can be identified through PCR which identifies bacterial DNA, but this is also not commonly done.

Treatment can be done with single-dose therapy using azithromycin or ceftriaxone or with multiple-dose therapy using cipro-flox-acin or erythromycin.##SummaryAlright, as a quick recap.

Haemophilus ducreyi is a Gram-negative coccobacillus, non-motile, facultatively anaerobic, oxidase positive and catalase negative.

It requires special conditions and mediums to grow, such as chocolate agar with factor X, and grows into small, grey or translucent colonies.

It has a bunch of virulence factors such as a capsule with antiphag-ocytic role, fimbria-like proteins and LOS for adherence to epithelial cells and fibroblasts, toxins such as cytolethal distending toxin and cytotoxic hemolysin which cause damage to cells, and a zinc-copper superoxide dismutase which helps in survival of bacteria.

It causes a sexually transmitted disease, called chancroid, which is usually diagnosed on the basis of clinical findings such as one or more painful genital ulcers with tender suppurative inguinal adenopathy, and by excluding other genital ulcerative diseases, such as syphilis or herpes simplex virus infection and is treated with single-dose therapy using azithromycin or ceftriaxone or with multiple-dose therapy using ciprofloxacin or erythromycin.