Francisella

Taxobox
color = lightgrey
name = "Francisella"

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image_width = 240px
regnum = Bacteria
phylum = Proteobacteria
classis = Gamma Proteobacteria
ordo = Thiotrichales
familia = Francisellaceae
genus = "Francisella"
genus_authority = Dorofe'ev 1947
subdivision_ranks = Species
subdivision ="F. novicida"
"F. philomiragia"
"F. tularensis"

"Francisella" is a genus of pathogenic, Gram-negative bacteria. They are small coccobacillary or rod-shaped, non-motile organisms, which are also facultative intracellular parasites of macrophages.cite journal | author=Allen LA | title=Mechanisms of pathogenesis: evasion of killing by polymorphonuclear leukocytes | journal=Microbes Infect | year=2003 | pages=1329–35 | volume=5 | issue=14 | pmid=14613776 | doi=10.1016/j.micinf.2003.09.011] Strict aerobes, "Francisella" colonies bear a morphological resemblance to those of the genus "Brucella".cite book | author = Ryan KJ; Ray CG (editors) | title = Sherris Medical Microbiology | edition = 4th ed. | pages = 488–90 | publisher = McGraw Hill | year = 2004 | id = ISBN 0-8385-8529-9 ]

The genus was named in honor of American bacteriologist Edward Francis, who, in 1922, first recognized "F. tularensis" (then named "Bacterium tularensis") as the causative agent of tularemia.cite journal | author = Francis E | year = 1921 | title = Tularemia. I. The occurrence of tularemia in nature as a disease of man | journal = Public Health Rep | issue = 36 | pages = 1731–53 ]

Pathogenesis

The type species, "F. tularensis", causes the disease tularemia or rabbit fever.cite book | author = Collins FM | title = Pasteurella, Yersinia, and Francisella. "In:" Baron's Medical Microbiology "(Baron S "et al", eds.)| edition = 4th ed. | publisher = Univ of Texas Medical Branch | year = 1996 | url = http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mmed.section.1624 | id = ISBN 0-9631172-1-1 ] "F. novicida" and "F. philomiragia" (previously "Yersinia philomiragia") are associated with septicemia and invasive systemic infections. It should be noted that the taxonomy of the genus is somewhat uncertain, especially in the case of "F. novicida" (may be a subspecies of "F. tularensis"). In general, identification of species is accomplished by biochemical profiling or 16S rRNA sequencing.

Laboratory characteristics

"Francisella" can survive for several weeks in the environment; paradoxically, they can be difficult to culture and maintain in the lab.cite journal |author=Ellis J, Oyston P, Green M, Titball R |title=Tularemia |journal=Clin Microbiol Rev |volume=15 |issue=4 |pages=631–46 |year=2002 |pmid=12364373 |doi=10.1128/CMR.15.4.631-646.2002] Growth is slow (though increased by CO₂ supplementation) and the organisms are fastidious, with most "Francisella" strains requiring cystine and cysteine media supplementation for growth. Growth has been successful on several media types, including chocolate agar and Thayer-Martin media with appropriate additives as noted above. Attempted isolation on MacConkey agar is not reliable or generally successful.

After 24 hours of incubation on appropriate solid media, "Francisella" colonies are generally small (1 to 2 mm), opaque, and white-gray to bluish-gray in color. Colonies are smooth, with clean edges and, after a 48 hours of growth, tend to have a shiny surface.

References

External links

* [http://www.biohealthbase.org/GSearch/statsAutomation.do?decorator=Francisella BioHealthBase Bioinformatics Resource Center] The National Institute of Allergy and Infectious Disease (NIAID) supports a public database describing the molecular genetics of "F. tularensis". The website describes the genes, proteins, and cellular characteristics of the pathogen.
* [http://observer.guardian.co.uk/foodmonthly/story/0,,1761837,00.html Francisella in Cod]