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Treponema pallidum is a spirochaete bacterium with subspecies that cause the diseases syphilis, bejel, and yaws. It is a helically coiled microorganism usually 6–15 µm long and 0.1–0.2 µm wide.[1] The treponemes have a cytoplasmic and an outer membrane. Using light microscopy, treponemes are visible only by using dark field illumination. They are Gram negative, but some regard them as too thin to be Gram stained.

Subspecies

Three subspecies of T. pallidum are known:[2]

  • Treponema pallidum pallidum, which causes syphilis
  • T. p. endemicum, which causes bejel or endemic syphilis
  • T. p. pertenue, which causes yaws

These bacteria were originally classified as members of separate species, but their close genetic relationship as demonstrated by DNA hybridization analysis indicated they were members of the same species. Treponema carateum, the cause of pinta, remains a separate species because no isolate is available for DNA analysis.[3]

Laboratory identification

Micrograph showing T. pallidum (black and thin) – Dieterle stain

This bacterium can be detected with special stains, such as the Dieterle stain. T. pallidum is also detected by serology, including nontreponemal VDRL, rapid plasma reagin, treponemal antibody tests (FTA-ABS), T. pallidum immobilization reaction, and syphilis TPHA test.[4] It was first microscopically identified in syphilitic chancres by Fritz Schaudinn and Erich Hoffmann at the Charité in Berlin in 1905.[5]

Clinical significance

T. p. 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. p. pallidum allows it to move in a corkscrew motion through mucous membranes or enter minuscule breaks in the skin. In women the initial lesion is usually on the labia, the walls of the vagina, or the cervix; in men it is on the shaft or glans of the penis.[6] It gains access to the host's blood and lymph systems through tissue and mucous membranes. In more severe cases, it may gain access to the host by infecting the skeletal bones and central nervous system of the body.

The three subspecies causing yaws, pinta, and bejel, which often cause lesions on the skin and mucous membranes as well as on soft tissue and bone,[7] are morphologically and serologically indistinguishable from T. p. pallidum (syphilis); however, their transmission is not venereal and the course of each disease is significantly different.[8]

The incubation period for a T. p. pallidum infection is usually around 21 days, but can range from 10 days to 90 days.[9]

Genome

The genome of T. pallidum was sequenced in 1998.[10] The recent sequencing of the genomes of several spirochetes permits a thorough analysis of the similarities and differences within this bacterial phylum. T. p. pallidum has one of the smallest bacterial genomes at 1.14 million base pairs, and has limited metabolic capabilities, reflecting its adaptation through genome reduction to the rich environment of mammalian tissue. The shape of T. pallidum is flat and wavy, unlike the other spirochetes, which are helical.[11]

Vaccine

No vaccine for syphilis is available as of 2017. 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,[12] and because T. pallidum outer membrane proteins have not been unambiguously identified.[13] [14]

References

  1. ^ Radolf, Justin D. (1996-01-01). Baron, Samuel, ed. Medical Microbiology (4th ed.). Galveston (TX): University of Texas Medical Branch at Galveston. ISBN 0963117211. PMID 21413263. 
  2. ^ Marks M, Solomon AW, Mabey DC (October 2014). "Endemic treponemal diseases". Transactions of the Royal Society of Tropical Medicine and Hygiene. 108 (10): 601–7. doi:10.1093/trstmh/tru128. PMC 4162659Freely accessible. PMID 25157125. 
  3. ^ Giacani L, Lukehart SA (January 2014). "The endemic treponematoses". Clinical Microbiology Reviews. 27 (1): 89–115. doi:10.1128/CMR.00070-13. PMC 3910905Freely accessible. PMID 24396138. 
  4. ^ Fisher, Bruce; Harvey, Richard P.; Champe, Pamela C. Lippincott's Illustrated Reviews: Microbiology (Lippincott's Illustrated Reviews Series). Hagerstown, MD: Lippincott Williams & Wilkins. ISBN 0-7817-8215-5. 
  5. ^ Schaudinn, Fritz Richard; Hoffmann, Erich (1905). "Vorläufiger Bericht über das Vorkommen von Spirochaeten in syphilitischen Krankheitsprodukten und bei Papillomen" [Preliminary report on the occurrence of Spirochaetes in syphilitic chancres and papillomas]. Arbeiten aus dem Kaiserlichen Gesundheitsamte. Berlin: Verlag von Julius Springer. 22: 527–534. 
  6. ^ https://www.ncbi.nlm.nih.gov/books/NBK7716/
  7. ^ Radolf, Justin D. (1996-01-01). Baron, Samuel, ed. Medical Microbiology (4th ed.). Galveston (TX): University of Texas Medical Branch at Galveston. ISBN 0963117211. PMID 21413263. 
  8. ^ https://www.ncbi.nlm.nih.gov/books/NBK7716/
  9. ^ "STD Facts – Syphilis (Detailed)". www.cdc.gov. Retrieved 2017-04-19. 
  10. ^ Fraser CM, Norris SJ, Weinstock GM, et al. (July 1998). "Complete genome sequence of Treponema pallidum, the syphilis spirochete". Science. 281 (5375): 375–88. doi:10.1126/science.281.5375.375. PMID 9665876. 
  11. ^ Clark, D.P., Dunlap, P.V, Madigan, J.T., Martinko, J.M. Brock Biology of Microorganism. San Francisco: Pearson. 2009. 79 p.
  12. ^ Bishop, Nancy H.; Miller, James N. (1976-07-01). "Humoral Immunity in Experimental Syphilis". The Journal of Immunology. 117 (1): 191–196. ISSN 0022-1767. PMID 778261. 
  13. ^ Tomson FL, Conley PG, Norgard MV, Hagman KE (September 2007). "Assessment of cell-surface exposure and vaccinogenic potentials of Treponema pallidum candidate outer membrane proteins". Microbes Infect. 9 (11): 1267–75. doi:10.1016/j.micinf.2007.05.018. PMC 2112743Freely accessible. PMID 17890130. 
  14. ^ Cameron CE, Lukehart SA (2014). "Current status of syphilis vaccine development: Need, challenges, prospects". Vaccine. 32 (14): 1602–1609. doi:10.1016/j.vaccine.2013.09.053. PMC 3951677Freely accessible. PMID 24135571. 

Further reading

External links

  • "Syphilis- CDC Fact Sheet." Centers for Disease Control and Prevention. May. 2004. Centers for Disease Control and Prevention. 7 February 2006