Intracellular parasite

Intracellular parasites are parasitic microorganisms - microparasites that are capable of growing and reproducing inside the cells of a host.

Facultative

Facultative intracellular parasites are capable of living and reproducing either inside or outside cells.

Bacterial examples include:

Fungal examples include:

Obligate

Two apicomplexans, Toxoplasma gondii, within their host cell. Transmission electron microscopy

Obligate intracellular parasites cannot reproduce outside their host cell, meaning that the parasite's reproduction is entirely reliant on intracellular resources.

Obligate intracellular parasites of humans include:

The mitochondria in eukaryotic cells may also have originally been such parasites, but ended up forming a mutualistic relationship (endosymbiotic theory).

Study of obligate pathogens is difficult because they cannot usually be reproduced outside the host. However, in 2009 scientists reported a technique allowing the Q-fever pathogen Coxiella burnetii to grow in an axenic culture and suggested the technique may be useful for study of other pathogens.[9]

Nutrition

The majority of intracellular parasites must keep host cells alive as long as possible while they are reproducing and growing. In order to grow they need nutrients that might be scarce in their free form in the cell. To study the mechanism that intracellular parasites use to obtain nutrients Legionella pneumophila, a facultative intracellular parasite, has been used as a model. It is known that Legionella pneumophila obtains nutrients by promoting host proteasomal degradation. Self-degradation of host proteins into amino acids provides the parasite with its primary carbon and energy source.[10]

Susceptibility

People with T cell deficiencies are particularly susceptible to intracellular pathogens.[11]

References

  1. ↑ Jantsch, J.; Chikkaballi, D.; Hensel, M. (2011). "Cellular aspects of immunity to intracellular Salmonella enterica". Immunological Reviews 240 (1): 185–195. doi:10.1111/j.1600-065X.2010.00981.x. PMID 21349094.
  2. ↑ Kelly, B. G.; Wall, D. M.; Boland, C. A.; Meijer, W. G. (2002). "Isocitrate lyase of the facultative intracellular pathogen Rhodococcus equi". Microbiology (Reading, England) 148 (Pt 3): 793–798. PMID 11882714.
  3. ↑ Spinosa MR, Progida C, Talà A, Cogli L, Alifano P, Bucci C (July 2007). "The Neisseria meningitidis capsule is important for intracellular survival in human cells". Infect. Immun. 75 (7): 3594–603. doi:10.1128/IAI.01945-06. PMC 1932921. PMID 17470547.
  4. ↑ Sebghati TS, Engle JT, Goldman WE (November 2000). "Intracellular parasitism by Histoplasma capsulatum: fungal virulence and calcium dependence". Science 290 (5495): 1368–72. doi:10.1126/science.290.5495.1368. PMID 11082066.
  5. ↑ Alvarez, M.; Burns, T.; Luo, Y.; Pirofski, L. A.; Casadevall, A. (2009). "The outcome of Cryptococcus neoformans intracellular pathogenesis in human monocytes". BMC Microbiology 9: 51. doi:10.1186/1471-2180-9-51. PMC 2670303. PMID 19265539.
  6. ↑ Amann R, Springer N, Schönhuber W, et al. (January 1997). "Obligate intracellular bacterial parasites of acanthamoebae related to Chlamydia spp". Applied and Environmental Microbiology 63 (1): 115–21. PMC 168308. PMID 8979345.
  7. ↑ Deng, M.; Lancto, C. A.; Abrahamsen, M. S. (2004). "Cryptosporidium parvum regulation of human epithelial cell gene expression". International Journal for Parasitology 34 (1): 73–82. doi:10.1016/j.ijpara.2003.10.001. PMID 14711592.
  8. ↑ Page 28 in: Title: Rook's textbook of dermatology, Volume 4, Rook's Textbook of Dermatology, Tony Burns (FRCP.) Authors: Arthur Rook, Tony Burns (FRCP.) Edition: 8 Publisher: John Wiley and Sons, 2010 ISBN 1-4051-6169-8, ISBN 978-1-4051-6169-5
  9. ↑ Omsland, Anders; Cockrell, Diane C.; Howe, Dale; Fischer, Elizabeth R.; Virtaneva, Kimmo; Sturdevant, Daniel E.; Porcella, Stephen F.; Heinzen, Robert A. (Mar 17, 2009). "Host cell-free growth of the Q fever bacterium Coxiella burnetii". Proceedings of the National Academy of Sciences USA 106 (11): 4430–4. doi:10.1073/pnas.0812074106. PMC 2657411. PMID 19246385. Retrieved September 18, 2011.
  10. ↑ Heuner K; Swanson M (editors). (2008). Legionella: Molecular Microbiology. Caister Academic Press.
  11. ↑ Page 432, Chapter 22, in: Jones, Jane; Bannister, Barbara A.; Gillespie, Stephen H. (2006). Infection: Microbiology and Management. Wiley-Blackwell. ISBN 1-4051-2665-5.
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