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 Francisella tularensis and Listeria monocytogenes. Other examples include Brucella, Legionella, Mycobacterium, and Yersinia. The gram negative bacterium Neisseria meningitidis can reproduce intracellularly but is not obligate.^[1]

A fungal example is Histoplasma capsulatum.^[2]

Obligate

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:

• Viruses
• Certain bacteria, including:
  • Chlamydia, and closely related species.^[3]
  • Rickettsia
  • Coxiella
  • Certain species of Mycobacterium such as Mycobacterium leprae
• Certain protozoa, including:
  • Plasmodia species
  • Leishmania spp.
  • Toxoplasma gondii
  • Trypanosoma cruzi

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.^[4]

References

1. ^ 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. http://iai.asm.org/cgi/pmidlookup?view=long&pmid=17470547. 
2. ^ 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. http://www.sciencemag.org/cgi/pmidlookup?view=long&pmid=11082066. 
3. ^ 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. http://aem.asm.org/cgi/pmidlookup?view=long&pmid=8979345. 
4. ^ Omsland, Anders; Cockrell, Diane C.; Howe, Dale; Fischer, Elizabeth R.; Virtaneva, Kimmo; Sturdevant, Daniel E.; Porcella, Stephen F.; Heinzen, Robert A. (2009 Mar 17). "Host cell-free growth of the Q fever bacterium Coxiella burnetii". Proceedings of the National Academy of Science USA 106 (11): 4430-4. http://www.ncbi.nlm.nih.gov/pubmed/19246385. Retrieved September 18, 2011.