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Intracellular parasite

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


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

Bacterial examples include:

Fungal examples include:


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).[citation needed]

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]


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. Thus we know that Legionella pneumophila obtains nutrients by promoting host proteasomal degradation. Self-degradation of host proteins into amino acids provides the parasite the primary carbon and energy source.[10]


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


  1. ^ Attention: This template ({{cite pmid}}) is deprecated. To cite the publication identified by PMID 21349094, please use {{cite journal}} with |pmid=21349094 instead.
  2. ^ Attention: This template ({{cite pmid}}) is deprecated. To cite the publication identified by PMID 11882714, please use {{cite journal}} with |pmid=11882714 instead.
  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. ^ Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.1186/1471-2180-9-51, please use {{cite journal}} with |doi=10.1186/1471-2180-9-51 instead.
  6. ^ 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.
  7. ^ Attention: This template ({{cite pmid}}) is deprecated. To cite the publication identified by PMID 14711592, please use {{cite journal}} with |pmid=14711592 instead.
  8. ^ 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.
  9. ^ 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 Science USA. 106 (11): 4430–4. doi:10.1073/pnas.0812074106. PMC 2657411. PMID 19246385.
  10. ^ Heuner K; Swanson M (editors). (2008). Legionella: Molecular Microbiology. Caister Academic Press.
  11. ^ Page 432, Chapter 22, in: Bannister, Barbara A.; Gillespie, Stephen H.; Jones, Jane (2006). Infection: Microbiology and Management. Wiley-Blackwell. ISBN 1-4051-2665-5.