Genus Rahnella
Cultural characteristics
Biochemical characters
Phylum Proteobacteria, Class Gammaproteobacteria, Order Enterobacteriales, Family Enterobacteriaceae, Genus Rahnella,  
Rahnella aquatilis - type species of the genus, Izard et al. 1981. Three genomospecies reported.
Gram-negative rods, 0.5–0.7 x 2–3 μm, non-motile or sometimes motile when growth
at 25 ºC.
S-type colonies, non-pigmented. Facultatively anaerobic, optimum growth
temperature 30-37 ºC; psychrotolerant - grows at 4 ºC. Media: Nutrient agar or nutrient
broth, Trypticase Soy Agar ± 5% sheep blood.
Widely distributed in nature. Isolated from water, foods (meat, freshwater fish, dairy products), plants, feces; from humans and animals
(snails, earthworms).
Isolated from immunocompromised human patients (blood, sputum, wound & burns infections, bacteremia).
Food contaminant. Rahnella contamination has been associated with increased histamine levels in fish products.
R. aquatilis grow symbiotically in plant root nodules (nitrogen-fixing bacteria) and express a  root adhesin and pore forming 38-kDa
major outer membrane protein. As the outer membrane protein shares high sequence similarity with those of other Gram-negative
pathogens, it seems possible that Rahnella's root adhesin mediates adherence to epithelial cells during bacterial invasion.
Also, O-lipopolysaccharide found to be toxic and pyogenic for experimental animals.
  1. J. G. Holt et al., 1994. Facultatively Anaerobic Gram-Negative Rods. Subgroup 1. Family Enterobacteriaceae. In: Begey’s Manual of
    Determinative Bacteriology, 9th-edition, Williams & Wilkins, pp 175-189.
  2. Izard D., Gavini F., Trinel P.A. & Leclerc H.: Rahnella aquatilis, nouveau membre de la famille des Enterobacteriaceae. Ann.
    Microbiol., 1979, 130A, 163-177.
  3. Brenner D.J., Muller H.E., Steigerwalt A.G., Whitney A.M., O'Hara C.M. & Kampfer P.: Two new Rahnella genomospecies that
    cannot be phenotypically differentiated from Rahnella aquatilis. Int. J. Syst. Bacteriol., 1998, 48, 141-149.
  4. Achouak, W., J.-M. Pages, R. De Mot, G. Molle, and T. Heulin. 1998. A major outer membrane protein of Rahnella aquatilis
    functions as a porin and root adhesin. J. Bacteriol. 180:909-913.
  5. Zdorovenko, E. L., L. D. Varbanets, G. V. Zatonsky, and A. N. Ostapchuk. 2004. Structure of the O-polysaccharide of the
    lipopolysaccharide of Rahnella aquatilis 1-95. Carbohydr. Res. 339:1809-1812.
  6. Varbanets, L. D., A. N. Ostapchuk, and N. V. Vinarskaia. 2004. Isolation and characterization of Rahnella aquatilis
    lipopolysaccharides. Mikrobiol. Zh. 66:25-34.
  7. Kaley Tash: Rahnella aquatilis Bacteremia from a Suspected Urinary Source. Journal of Clinical Microbiology, May 2005, p. 2526-
    2528, Vol. 43, No. 5.
  8. Don J. Brenner & J.J. Farmer III, 2004, Family I. Enterobacteriaceae, In: Bergey’s Manual of Systematic Bacteriology, Second
    edition, Vol two, part B, George M. Garrity (Editor-in-Chief), pp. 740-744.
R. aquatilis may be confused with Enterobacter agglomerans due to similarities in the
organisms' biochemical tests.
The three genomospecies of
Rahnella aquatilis cannot be biochemically differentiated.

Positive results for nitrates reduction, catalase, beta-galactosidase, phenylalanine deaminase (in 48 h), methyl red, Voges –
Proskauer reaction, citrate utilization, malonate utilization, esculin hydrolysis, acid production from: L-arabinose, cellobiose, lactose,
maltose, mannose, L-rhamnose, raffinose, D-xylose and salicin.

Negative results for oxidase, lysine decarboxylase, ornithine decarboxylase, arginine dihydrolase, indole production, H
2S production,
urea hydrolysis, gelatin hydrolysis, DN-ase, lipase, acetate utilization, acid production from myo-inositol, alpha-methyl-D-glucoside,  
adonitol, D-arabitol and erythritol.

Variable results for acid production from glycerol, dulcitol and mucate.
(c) Costin Stoica
Culture media
Biochemical tests
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