# Francisella

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{{Short description|Genus of bacteria}}
{{Automatic taxobox
| image = Francisella_tularensis_01.jpg
| parent_authority = Sjöstedt 2005
| taxon = Francisella
| authority = Dorofe'ev 1947
| subdivision_ranks = Species
| subdivision =
''[F. tularensis](/source/Francisella_tularensis)''<br />
''[F. novicida](/source/Francisella_novicida)''<br />
''[F. hispaniensis](/source/Francisella_hispaniensis)''<br />
''[F. persica](/source/Francisella_persica)''<br />
''[F. noatunensis](/source/Francisella_noatunensis)''<br />
''[F. philomiragia](/source/Francisella_philomiragia)''<br />
''[F. halioticida](/source/Francisella_halioticida)''<br />
''[F. endociliophora](/source/Francisella_endociliophora)''<br />
''[F. guangzhouensis](/source/Francisella_guangzhouensis)'' <br />
''[F. piscicida](/source/Francisella_piscicida)''
}}

'''''Francisella''''' is a [genus](/source/genus) of [Gram-negative](/source/Gram-negative) [bacteria](/source/bacterium). They are small [coccobacillary](/source/coccobacillus) or [rod-shaped](/source/bacillus), non[motile](/source/Motility) organisms, which are also facultative [intracellular](/source/intracellular) parasites of [macrophage](/source/macrophage)s.<ref name=Allen_2003>{{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| doi-access=free }}</ref> Strict [aerobes](/source/Aerobic_organism), ''Francisella'' colonies bear a morphological resemblance to those of the genus ''[Brucella](/source/Brucella)''.<ref name=Sherris>{{cite book | editor = Ryan KJ | editor2 = Ray CG | title = Sherris Medical Microbiology | edition = 4th | pages = 488&ndash;90 | publisher = McGraw Hill | year = 2004 | isbn = 0-8385-8529-9 }}</ref> Some ''Francisella'' species are pathogenic bacteria but some others are [endosymbiont](/source/endosymbiont)s of ticks.<ref name=":0">{{Cite journal |last1=Duron |first1=Olivier |last2=Morel |first2=Olivier |last3=Noël |first3=Valérie |last4=Buysse |first4=Marie |last5=Binetruy |first5=Florian |last6=Lancelot |first6=Renaud |last7=Loire |first7=Etienne |last8=Ménard |first8=Claudine |last9=Bouchez |first9=Olivier |last10=Vavre |first10=Fabrice |last11=Vial |first11=Laurence |date=2018-06-18 |title=Tick-Bacteria Mutualism Depends on B Vitamin Synthesis Pathways |journal=Current Biology |language=English |volume=28 |issue=12 |pages=1896–1902.e5 |doi=10.1016/j.cub.2018.04.038 |issn=0960-9822 |pmid=29861133|s2cid=44095809 |doi-access=free }}</ref> Ticks do not use any other food source than vertebrate blood and therefore  ingest high levels of protein, iron and salt, but few vitamins. To overcome these nutritional deficiencies, ticks have evolved obligate interactions with nutritional endosymbionts, including ''Francisella'' endosymbionts. Their experimental elimination typically results in decreased tick survival, molting, fecundity and egg viability, as well as in physical abnormalities, which all are fully restored with an oral supplement of [B vitamin](/source/B_vitamin)s.<ref name=":0" /> The genome sequencing of ''Francisella'' endosymbionts confirmed that they consistently produce three B vitamin types, [biotin](/source/biotin) (vitamin B<sub>7</sub>), [riboflavin](/source/riboflavin) (B<sub>2</sub>) and [folate](/source/folate) (B<sub>9</sub>).<ref>{{Cite journal |last1=Duron |first1=Olivier |last2=Gottlieb |first2=Yuval |date=2020-10-01 |title=Convergence of Nutritional Symbioses in Obligate Blood Feeders |journal=Trends in Parasitology |language=English |volume=36 |issue=10 |pages=816–825 |doi=10.1016/j.pt.2020.07.007 |issn=1471-4922 |pmid=32811753|s2cid=221181791 |doi-access=free |url=https://hal.archives-ouvertes.fr/hal-03000781/file/Duron%20%26%20Gottlieb%20TIP%20May11_edited_revised.pdf }}</ref> ''Francisella'' endosymbionts are often misidentified as ''[Francisella tularensis](/source/Francisella_tularensis)''; however, ''Francisella'' endosymbionts lack virulence genes and cannot infect humans.<ref>{{Cite journal |last1=Buysse |first1=Marie |last2=Duron |first2=Olivier |date=2021-04-29 |title=Evidence that microbes identified as tick-borne pathogens are nutritional endosymbionts |journal=Cell |language=English |volume=184 |issue=9 |pages=2259–2260 |doi=10.1016/j.cell.2021.03.053 |issn=0092-8674 |pmid=33930290|s2cid=233471930 |doi-access=free }}</ref>

The genus was named in honor of American [bacteriologist](/source/microbiology) [Edward Francis](/source/Edward_Francis_(bacteriologist)), who, in 1922, first recognized ''F. tularensis'' (then named ''Bacterium tularensis'') as the causative agent of [tularemia](/source/tularemia).<ref name=Francis>{{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 | doi = 10.2307/4576069 | jstor = 4576069 }}</ref>

== Pathogenesis ==
The type species, ''[F. tularensis](/source/Francisella_tularensis)'', causes the disease tularemia or rabbit fever.<ref name=Baron>{{cite book | author = Collins FM | title =  Pasteurella, Yersinia, and Francisella. In: ''Baron's Medical Microbiology'' (Baron S ''et al.'', eds.)| edition = 4th | publisher = Univ of Texas Medical Branch | year = 1996 | url = https://www.ncbi.nlm.nih.gov/books/NBK7798/ | isbn = 0-9631172-1-1 }}</ref> ''[F. novicida](/source/Francisella_novicida)'' and ''[F. philomiragia](/source/Francisella_philomiragia)'' (previously ''Yersinia philomiragia'') are associated with [sepsis](/source/sepsis) and invasive systemic infections.

Francisella has been detected in ticks <ref>Vilcins I, Fournier P, Old JM, Deane EM (2009). Evidence for the presence of Francisella and spotted fever group Rickettsia DNA in the Tick ''Amblyomma fimbriatum'' (Acari: Ixodidae), Northern Territory, Australia. Journal of Medical Entomology. 46(4), 926-933. doi:  10.1186/s13071-015-0719-3 </ref>

== Taxonomy ==
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](/source/16S_ribosomal_RNA) [rRNA](/source/rRNA) sequencing. An updated phylogeny based on whole genome sequencing has recently been published showing the genus ''Francisella'' could be divided into two main genetic clades: one including ''F. tularensis'', ''F. novicida'' and ''[F. hispaniensis](/source/Francisella_hispaniensis)'', and another including ''[F. philomiragia](/source/Francisella_philomiragia)'' and ''[F. noatunensis](/source/Francisella_noatunensis)''.<ref name=Sjodin_2012>{{cite journal |vauthors=Sjödin A, Svensson K, Öhrman C, Ahlinder J, Lindgren P, Duodu S, Johansson A, Colquhoun DJ, Larsson P, Forsman M |title=Genome characterisation of the genus Francisella reveals insight into similar evolutionary paths in pathogens of mammals and fish |journal=BMC Genomics |volume=13 |issue=268  |year=2012 |pmid=22727144 |doi=10.1186/1471-2164-13-268 |pmc=3485624 |pages=268 |doi-access=free }}</ref>

== Laboratory characteristics ==
''Francisella'' species can survive for several weeks in the environment; paradoxically, they can be difficult to culture and maintain in the laboratory.<ref name=Ellis_2002>{{cite journal |vauthors=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 |pmc=126859}}</ref> Growth is slow (though increased by [CO<sub>2</sub>](/source/Carbon_dioxide) supplementation) and the organisms are [fastidious](/source/Growth_medium), with most ''Francisella'' strains requiring [cystine](/source/cystine) and [cysteine](/source/cysteine) media supplementation for growth. Growth has been successful on several media types, including [chocolate agar](/source/chocolate_agar) and [Thayer–Martin medium](/source/Thayer%E2%80%93Martin_agar) with appropriate additives as noted above. Attempted isolation on [MacConkey agar](/source/MacConkey_agar) is '''not''' reliable or generally successful.<ref name=Baron/>

After 24 hours of incubation on appropriate solid media, ''Francisella'' colonies are generally small (1 to 2&nbsp;mm), [opaque](/source/Opacity_(optics)), 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 ==
{{Reflist}}

== External links ==
* [https://patricbrc.org/view/Taxonomy/262#view_tab=overview Francisella] genomes and related information at [http://patricbrc.org/   PATRIC], a Bioinformatics Resource Center funded by [https://www.niaid.nih.gov/   NIAID]
* [https://www.theguardian.com/lifeandstyle/2006/apr/30/foodanddrink.features7 Francisella in Cod]

{{Taxonbar|from=Q3246268}}
{{Authority control}}

Category:Thiotrichales
Category:Bacteria genera

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Adapted from the Wikipedia article [Francisella](https://en.wikipedia.org/wiki/Francisella) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Francisella?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.