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Treponema pallidum

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Taxonomy

Treponema pallidum belongs to the only order Spirochaetales in class of bacteria Spirochaetes. All spirochetes are helical or spiral shaped microorganisms. Spirochetes are highly motile and propel themselves in corkscrew manner by rotating around their longitudinal axes. These organisms can swim easily through gel-like materials that hinder most other flagellated organisms, which allow some spirochetes to occupy unique ecological niches, such as sediments in pond and lake bottoms, the guts of certain arthropods, and the rumens of cows and sheep. The arrangement of spirochete flagella is also unique among the bacteria. The flagella are inserted subterminally at each end of the cell, wrap around the protoplasmic cylinder, and usually overlap in the center region. They are located between the protoplasmic cylinder and an outer membrane-like structure called the outer sheath and called endoflagella or periplasmic flagella. All spirochetes are resistant to the antibiotic rifamycin. The order is divided into three major families Brachyspiraceae, Leptospiraceae, and Spirochaetaceae. Treponema pallidum is classified into Spirochaetaceae, the family that apart of genus Treponema also contains genera Borrelia (contains causative agents of Lyme disease and relapsing fever), Cristispira (found in digestive tract of bivalve mollusks), Spirochaeta (free-living spirochetes), Brevinema (infectious in some animals), Brachyspira (pathogenic in swine and chicken), and Spironema (found in mosquito).
Borrelia burgdorferi, Lyme disease spirochete taxonomy, facts, pathogenicity, and bibliography at MetaPathogen

cellular organisms - Bacteria - Spirochaetes - Spirochaetes (class) - Spirochaetales - Spirochaetaceae - Treponema - Treponema pallidum - Treponema pallidum subsp. pallidum

Brief facts

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Biology of Treponema pallidum subsp. pallidum

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Evasion of host immune defenses

For a long time researchers tried to explain mechanisms underlying the natural course of the syphilis: recurring clinical manifestations separated by prolonged asymptomatic periods. In early 1970s it was believed that treponemes cause specific or generalized immunosuppression and are resistant to phagocytosis by macrophages and neutrophils. Later studies showed, however, that initial immune response of host to treponemal assault, though slow to develop, is rather robust, and as treponemes reach peak numbers, macrophages begin to infiltrate the lesions resulting in rapid clearance of overwhelming majority of the parasites from the tissue. However, some portion of the treponemes remains untouched and continues living in the host causing a persistent infection.

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Immune response to early syphilis

Immune response to early syphilis

 

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Stages of syphilis

Untreated patients survive as long as 50 years after infection. Syphilis is also called the "great imitator" because manifestations of the disease on various stages imitate a variety of skin and mental diseases. Atypical presentations of the syphilis became more frequent nowadays due to medicamentous interferences (antibiotics, metronidazole, and anti-inflammatory medications, etc.), chronic alcoholism, chronic infections (for example, AIDS) and elderly age.

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Treatment of syphilis

Penicillin therapy for syphilis became available in 1950s. Penicillin still remains the drug of choice in syphilis treatment. Several T. pallidum proteins have been shown to bind penicillin. Penicillin-binding proteins often function in cell wall synthesis pathways; thus, penicillin kills susceptible bacteria by interfering with production of cell walls. Recently, one penicillin-binding protein, TpN47, was shown to have beta-lactamase activity; paradoxically, this activity is inhibited by the products of the reaction and the organism remains penicillin sensitive. Guidelines published by the Centers for Disease Control and Prevention specify oral doxycycline or tetracycline as alternative treatments in the case of penicillin allergy (except for pregnant women).

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Features associated with HIV/syphilis co-infection

Syphilis infection increases the risk of transmitting and acquiring HIV infection. Not only are syphilis lesions a portal of entry for HIV but the immune cells that carry and are successful to the virus, macrophages and T lymphocytes, are found in abundance in syphilis lesions. There is also some experimental evidence for direct involvement of T. pallidum in facilitating HIV infection and progression.

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References

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