Haemophilus ducreyi

A Microbial Biorealm page on the genus Haemophilus ducreyi

Classification

Higher order taxa

Bacteria; Proteobacteria; Gammaproteobacteria; Pasteurellales; Pasteurellaceae; [Others may be used. Use NCBI link to find]

Species

NCBI: Taxonomy

Coccobacillus ducreyi, Bacillus ulceris cancrosi, Haemophilus ducreyi

Description and significance

Haemophilus ducreyi causes the sexually transmitted disease, Chancroid. There has been renewed interest in this bacillus because of the close connections between Chancroid and Human Immunodeficiency Virus (HIV) infections. It typically grows on the male genitalia and causes a painful shallow ulcer at the site of infection. It is more common in African, Asian, and Latin American countries and is rarely seem in the US.

Haemophilus ducreyi was first described in 1889 by Auguste Ducrey The organism was isolated on artificial media a decade later but has remained difficult to isolate consistently. However novel methods of isolating these bacteria have been developed. It can grow well on a chocolate Agar supplemented with 1% Iso VitaleX and 5% sheep blood. Oxygen and high levels of carbon dioxide are preferable, and it needs to be grown in blood clot tubes in a humid atmosphere.

Genome structure

This bacterium consists of 1,698,955 base pairs and 1717 genes. It has a circular chromosome. There are 649,349 G+C base pairs, which accounts for 38.22% of the total base pairs. Also, 1,693 open reading frames were identified in this bacterium. Only 5 plasmid profiles have been identified out of 342 strains of Haemophilus ducreyi, however the characteristics of these plasmids are still being studied.

Cell structure and metabolism

Haemophilus ducreyi is a gram-negative, rod-shaped, anaerobic, non-motile, pathogenic bacillus. Unlike other Haemophila, H. ducreyi is unable to synthesize heme because it lacks the enzyme ferro-chelatase, which is used to catalyze the synthesis of heme by inserting ferrous iron into protoporphyrin IX. Its main source of heme is from hemoglobin, which is observed to be acquired through cell invasion. Some of the virulence determinants on the bacterium that are suspected to be responsible for ulcer formation in humans are lippligosacchride, pili, a hemolysin, a secreted toxin, an outer membrane hemoglobin binding protein, and a copper-zinc superoxide dismutase.

Some important molecules that are secreted by H. ducreyi include CDT. Cytolethal distending toxin (CDT) is also secreted and could be the cause of the generation and slow healing of ulcers. The bacterium also causes the host to secrete Interleukin 8 (IL-8) and IL-6, potent chemoattractants for neutrophils that may be important in infection.

Pathology

The way that H. ducreyi infects cells is that it enters the skin through wounds and stimulates keratinocytes, fibroblasts, endothelial cells, or melanocytes to secret IL-6 and IL-8. IL-8 leads to polymorphonuclear leukocytes (PMN) and macrophage accumulation in epidermis and dermis. IL-6 leads to IL-2 and IL-2 expression in T-cells. Thus this recruits CD4 to the abrasions. Fibrin and collagen deposits are part of the wound repair and act as a matrix for the PMNs and macrophages. Lipoproteins and lippligosacchride (LOS) activate macrophages to make IL-12 and TNF-α which works with chemokines. IFN- γ, which is produced by T cells, and TNF- α allow keratinocytes to make IL-8 and other chemokines which amplify the process. Inflammatory cytokines and bacterial products migrate to lymph nodes where T cells naïve to H. ducreyi antigens are sensitized. Memory T-cells specific to H. ducredyi then go to the lesion. When PMN’s and macrophages fail to clear the organism type 1 immunity is sustained and its products continue to form. The products from type 1 immunity damage the skin, this is why chancroid is a type of immunopathogenesis.

Symptoms of chancroid start with a small bump that becomes an ulcer within a day of its appearance. The ulcer ranges between 1/8 to 2 inches in size, it is painful, it has irregular or ragged borders, the base is covered with grayish or yellowish material, and it easily bleeds if traumatized. Ulcers most commonly form on the foreskin of the penis and on the groove behind the head of the penis.