Treponema pallidum

Treponema pallidum
Scientific classification
Domain:Bacteria
Phylum:Spirochaetes
Order:Spirochaetales
Family:Spirochaetaceae
Genus:Treponema
Species: T. pallidum
Binomial name
Treponema pallidum

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.

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.[1] 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,[1] 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.[1]

The incubation period for a T. p. pallidum infection is usually around 21 days, but can range from 10 days to 90 days.[6]

Genome

The genome of T. pallidum was sequenced in 1998.[7] The recent sequencing of the genomes of several spirochetes permits a thorough analysis of the similarities and differences within this bacterial phylum and within the species.[8][9][10] 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] In contrast, some of the known antigens are intracellular and antibody against them are ineffective to clear the infection.[15][16][17]

References

  1. 1 2 3 4 Radolf JD (1996). Baron S, 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 4162659. 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 3910905. PMID 24396138.
  4. ↑ Fisher B, Harvey RP, Champe PC. Lippincott's Illustrated Reviews: Microbiology (Lippincott's Illustrated Reviews Series). Hagerstown, MD: Lippincott Williams & Wilkins. ISBN 0-7817-8215-5.
  5. ↑ Schaudinn FR, Hoffmann E (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. ↑ "STD Facts – Syphilis (Detailed)". Centers for Disease Control (CDC). Retrieved 2017-04-19.
  7. ↑ Fraser CM, Norris SJ, Weinstock GM, White O, Sutton GG, Dodson R, 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.
  8. ↑ Zobaníková M, Mikolka P, Cejková D, Pospíšilová P, Chen L, Strouhal M, Qin X, Weinstock GM, Smajs D (October 2012). "Complete genome sequence of Treponema pallidum strain DAL-1". Standards in Genomic Sciences. 7 (1): 12–21. doi:10.4056/sigs.2615838. PMC 3570794. PMID 23449808.
  9. ↑ Tong ML, Zhao Q, Liu LL, Zhu XZ, Gao K, Zhang HL, Lin LR, Niu JJ, Ji ZL, Yang TC (2017). "Whole genome sequence of the Treponema pallidum subsp. pallidum strain Amoy: An Asian isolate highly similar to SS14". PLOS One. 12 (8): e0182768. doi:10.1371/journal.pone.0182768. PMC 5546693. PMID 28787460.
  10. ↑ Seshadri R, Myers GS, Tettelin H, Eisen JA, Heidelberg JF, Dodson RJ, et al. (April 2004). "Comparison of the genome of the oral pathogen Treponema denticola with other spirochete genomes". Proceedings of the National Academy of Sciences of the United States of America. 101 (15): 5646–51. doi:10.1073/pnas.0307639101. PMC 397461. PMID 15064399.
  11. ↑ Clark DP, Dunlap PV, Madigan JT, Martinko JM (2009). Brock Biology of Microorganisms. San Francisco: Pearson. p. 79.
  12. ↑ Bishop NH, Miller JN (July 1976). "Humoral immunity in experimental syphilis. I. The demonstration of resistance conferred by passive immunization". Journal of Immunology. 117 (1): 191–6. 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 and Infection. 9 (11): 1267–75. doi:10.1016/j.micinf.2007.05.018. PMC 2112743. PMID 17890130.
  14. ↑ Cameron CE, Lukehart SA (March 2014). "Current status of syphilis vaccine development: need, challenges, prospects". Vaccine. 32 (14): 1602–9. doi:10.1016/j.vaccine.2013.09.053. PMC 3951677. PMID 24135571.
  15. ↑ Penn CW, Bailey MJ, Cockayne A (April 1985). "The axial filament antigen of Treponema pallidum". Immunology. 54 (4): 635–41. PMC 1453562. PMID 3884491.
  16. ↑ Norris SJ (September 1993). "Polypeptides of Treponema pallidum: progress toward understanding their structural, functional, and immunologic roles. Treponema Pallidum Polypeptide Research Group". Microbiological Reviews. 57 (3): 750–79. PMID 8246847.
  17. ↑ Izard J, Renken C, Hsieh CE, Desrosiers DC, Dunham-Ems S, La Vake C, Gebhardt LL, Limberger RJ, Cox DL, Marko M, Radolf JD (December 2009). "Cryo-electron tomography elucidates the molecular architecture of Treponema pallidum, the syphilis spirochete". Journal of Bacteriology. 191 (24): 7566–80. doi:10.1128/JB.01031-09. PMC 2786590. PMID 19820083.

Further reading

  • Althouse BM, Hébert-Dufresne L (October 2014). "Epidemic cycles driven by host behaviour". Journal of the Royal Society, Interface. 11 (99): 20140575. doi:10.1098/rsif.2014.0575. PMC 4235258. PMID 25100316.
  • "Syphilis- CDC Fact Sheet." Centers for Disease Control and Prevention. May. 2004. Centers for Disease Control and Prevention. 7 February 2006
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