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Francisella tularensis

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Francisella tularensis is a Gram-negative bacteria that causes the disease tularemia. The Francisella genus also includes the species Francisella novicida and Francisella holarctica. Francisella are small rod- or rounded rod-shaped (coccobacillary or bacillus) bacteria. They are obligate aerobic, non-motile, facultative intracellular parasites.

Francisella tularensis as seen with Direct Fluorescent Antibody Stain (DFA). Source: CDC PHIL Image 1909 / Courtesy of Larry Stauffer, Oregon State Public Health Laboratory.

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History

The genus was named in honor of Edward Francis, the American microbiologist who, in 1922, first recognized tularemia in humans.[1][2]

Effect on Humans

Francisella tularensis causes the disease ]tularemia or rabbit fever. Francisella novicida and Francisella philomiragia are associated with blood infections (septicemia) and systemic infections. Differentiation of Francisella species is usually done by biochemical profiling or genetic (16S rRNA sequencing) analysis.

Laboratory characteristics

Although it can survive for several weeks in the environment; Francisella are difficult to culture and grow in laboratories.[3] Growth is slow (though increased by carbon dioxide (CO2) supplementation) and the organisms require special additives to the growth medium (fastidious). Growth has been successful on several media types, including chocolate agar and Thayer-Martin media with appropriate additives as noted above.

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

  1. ↑ Francis E, Tularemia. I. The occurrence of tularemia in nature as a disease of man.1921.Public Health Rep 36:1731–53.
  2. ↑ Hornick, R. Tularemia Revisited N Engl J Med 2001 345: 1637-1639 [http://content.nejm.org/cgi/content/full/345/22/1637 Full Text
  3. ↑ Ellis J, Oyston P, Green M, Titball R .Tularemia. Clin Microbiol Rev 15(4): 631–46.2002 Abstract [ http://dx.doi.org/10.1128/CMR.15.4.631-646.2002 Full Text]

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The content on or accessible through Medpedia.com is for informational purposes only. Medpedia is not a substitute for professional advice or expert medical services from a qualified health professional. Read more

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