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
H. ducreyi infects cells by entering the skin through wounds and stimulating keratinocytes, fibroblasts, endothelial cells, or melanocytes to secrete IL-6 and IL-8. While bacteria is definitely transferred from lesions, it is also suggested that bacteria can be transferred before lesions appear (Spinola et al, 1996). 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 recruiting CD4 to the abrasions. Fibrin and collagen deposits are part of the wound, they repair and act as a matrix for the PMNs and macrophages. Lipoproteins and lipooligosaccharide (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. ducreyi 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. H. ducreyi also produces a cytotoxin that kills HeLa and HEp-2 cells (Cope et al, 1997).
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, and 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.
References
Albritton, W. "Biology of Haemophilus ducreyi". Microbiol Rev. 1989. p. 377–389.
Edited by Anthony Nguyen, student(s) of Rachel Larsen at UCSD.
Edited KMG