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Intracellular parasite

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Intracellular parasites are microparasites that are capable of growing and reproducing inside the cells of a host. Some parasites can cause disease.


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

Bacterial examples include:

Fungal examples include:


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).[10]

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.[11]


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.[12] Self-degradation of host proteins into amino acids provides the parasite with its primary carbon and energy source.[13]


People with T cell deficiencies are particularly susceptible to intracellular pathogens.[14]

See alsoEdit


  1. ^ "Bartonella henselae" (PDF).
  2. ^ Dramsi, Shaynoor; Cossart, Pascale (2002-03-18). "Listeriolysin O". The Journal of Cell Biology. 156 (6): 943–946. doi:10.1083/jcb.200202121. ISSN 0021-9525. PMC 2173465. PMID 11901162.
  3. ^ 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.
  4. ^ Kelly, B. G.; Wall, D. M.; Boland, C. A.; Meijer, W. G. (2002). "Isocitrate lyase of the facultative intracellular pathogen Rhodococcus equi". Microbiology. 148 (Pt 3): 793–798. doi:10.1099/00221287-148-3-793. PMID 11882714.
  5. ^ Sebghati TS, Engle JT, Goldman WE (November 2000). "Intracellular parasitism by Histoplasma capsulatum: fungal virulence and calcium dependence". Science. 290 (5495): 1368–72. Bibcode:2000Sci...290.1368S. doi:10.1126/science.290.5495.1368. PMID 11082066.
  6. ^ 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.
  7. ^ Amann R, Springer N, Schönhuber W, Ludwig W, Schmid EN, Müller KD, Michel R (January 1997). "Obligate intracellular bacterial parasites of acanthamoebae related to Chlamydia spp". Applied and Environmental Microbiology. 63 (1): 115–21. PMC 168308. PMID 8979345.
  8. ^ 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.
  9. ^ David Anthony Burns; Stephen M. Breathnach; Neil H. Cox; Christopher E. M. Griffiths, eds. (2010). Rook's Textbook of Dermatology. Vol. 4 (8th ed.). Chichester: Wiley-Blackwell. p. 28. ISBN 978-1-4051-6169-5.
  10. ^ Lynn Sagan (1967). "On the origin of mitosing cells". J Theor Biol. 14 (3): 255–274. doi:10.1016/0022-5193(67)90079-3. PMID 11541392.
  11. ^ Omsland A, Cockrell DC, Howe D, Fischer ER, Virtaneva K, Sturdevant DE, Porcella SF, Heinzen RA (March 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. Bibcode:2009PNAS..106.4430O. doi:10.1073/pnas.0812074106. PMC 2657411. PMID 19246385.
  12. ^ Price, C. T. D; Al-Quadan, T; Santic, M; Rosenshine, I; Abu Kwaik, Y (2011). "Host Proteasomal Degradation Generates Amino Acids Essential for Intracellular Bacterial Growth". Science. 334 (6062): 1553–7. Bibcode:2011Sci...334.1553P. doi:10.1126/science.1212868. PMID 22096100.
  13. ^ Heuner K; Swanson M (editors). (2008). Legionella: Molecular Microbiology. Caister Academic Press.[page needed]
  14. ^ Bannister, Barbara A.; Gillespie, Stephen H.; Jones, Jane (2006). "Chapter 22". Infection: Microbiology and Management. Malden, MA: Wiley-Blackwell. p. 432. ISBN 1-4051-2665-5.