Treponema pallidum

Treponema pallidum
Scientific classification
Kingdom:	Eubacteria
Phylum:	Spirochaetes
Class:	Spirochaetes
Order:	Spirochaetales
Family:	Spirochaetaceae
Genus:	Treponema
Species:	T. pallidum
Binomial name
Treponema pallidum Schaudinn & Hoffmann, 1905

Treponema pallidum is a spirochaete bacterium. It is not seen on a Gram stained smear because the organism is too thin. Habitat: Human genital tract. Transmission by sexual contact and from mother to fetus across placenta.

Subspecies

There are at least four known subspecies:

• Treponema pallidum endemicum, which causes bejel
• T. pallidum carateum, which causes pinta
• T. pallidum pertenue, which causes yaws
• T. pallidum pallidum, which causes syphilis

There is some variation as to which are considered subspecies, and which are species. The cause of pinta is sometimes described as "Treponema carateum", rather than a subspecies of Treponema pallidum, even when the subspecies convention is used for the other agents.^[1]

Laboratory identification

This bacterium is too thin to be visualized with a standard Gram stain so two techniques to visualize it with a light microscope are dark field microscopy and immunofluorescence.

Treponema pallidum is also detected by serology, including nontreponemal (VDRL, Rapid plasma reagin (RPR) and treponemal antibody tests (FTA-ABS, Treponema pallidum immobilization reaction (TPI) and Syphilis TPHA test).^[2]

Clinical significance

T. pallidum pallidum is a motile spirochaete that is generally acquired by close sexual contact, entering the host via breaches in squamous or columnar epithelium. The organism can also be transmitted to a fetus by transplacental passage during the later stages of pregnancy, giving rise to congenital syphilis. The helical structure of T. pallidum pallidum allows it to move in a corkscrew motion through a viscous medium such as mucus. It gains access to host's blood and lymph systems through tissue and mucous membranes.

The subspecies causing yaws, pinta, and bejel are morphologically and serologically indistinguishable from T. pallidum pallidum (syphilis); however, their transmission is not venereal in nature and the course of each disease is significantly different.

Genome

In the July 17, 1998 issue of the journal Science, a group of biologists reported how they sequenced the genome of T. pallidum.^[3] The recent sequencing of the genomes of several spirochetes permits a thorough analysis of the similarities and differences within this bacterial phylum. Treponema pallidum subsp. pallidum has one of the smallest bacterial genomes at 1.14 million base pairs (Mb) and has limited metabolic capabilities, reflecting its adaptation through genome reduction to the rich environment of mammalian tissue.

Vaccine

There is no vaccine for syphilis. The outer membrane of T. pallidum has too few surface proteins for an antibody to be effective. Efforts to develop a safe and effective syphilis vaccine have been hindered by uncertainty about the relative importance of humoral and cellular mechanisms to protective immunity^{[citation needed]} and the fact that T. pallidum outer membrane proteins have not been unambiguously identified.^[4]

References

External links

• Bak, Matthew. "Treponema pallidum: The Etiologic Agent of Syphilis." 7 February 2006
• "Syphilis- CDC Fact Sheet." Centers for Disease Control and Prevention. May. 2004. Centers for Disease Control and Prevention. 7 February 2006