Discover

'''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. Mechanisms of pathogenesis: evasion of killing by polymorphonuclear leukocytes, Allen LA, , , Microbes Infect, 2003 Strict aerobes, ''Francisella'' colonies bear a morphological resemblance to those of the genus ''Brucella''. Sherris Medical Microbiology, Ryan KJ; Ray CG (editors), , , McGraw Hill, 2004, 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. Tularemia. I. The occurrence of tularemia in nature as a disease of man., Francis E, , , Public Health Rep, 1921

Contents

Pathogenesis

Laboratory characteristics

References

Web Links

Pathogenesis

The type species, ''F. tularensis'', causes the disease tularemia or rabbit fever. Pasteurella, Yersinia, and Francisella. ''In:'' Baron's Medical Microbiology ''(Baron S ''et al'', eds.), Collins FM, , , Univ of Texas Medical Branch, 1996, 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. Tularemia, Ellis J, Oyston P, Green M, Titball R, , , Clin Microbiol Rev, 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 medias 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

Web Links

★ 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.

★ Francisella in Cod