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.