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Phylum Firmicutes, Class Clostridia, Order Clostridiales, Family Clostridiaceae, Genus Clostridium, Cluster XIVa (Clostridium non
sensu stricto),
Clostridium innocuum  Smith and King 1962.
Gram-positive, straight rods, 0.4-1.6/1.6-9.4 µm, occur singly or in pairs. Nonmotile.
Spores are oval, terminal or subterminal or free and wider than the cell. Sporulation
usually occurs readily in chopped-meat broth cultures incubated for 24 hours or on
egg-yolk agar plates incubated for 48–72 hours.
Surface colonies on blood agar plates are 0.5–3 mm in diameter, circular, raised or
convex, translucent, gray-white or yellowish, smooth, and shiny, with a mottled or
mosaic internal structure and an entire or slightly scalloped margin. Hemolysis is
variable. Cultures in PYG broth are turbid with a smooth sediment and a pH of 4.7–5.2
after incubation for 24 hours.
Optimum temperature for growth is 37 ºC. Can grow at 25 and 45 ºC. Growth is
stimulated by fermentable carbohydrates. Growth is inhibited by 6.5% NaCl. Abundant
gas is detected in PYG deep agar cultures. Products in PYG broth are butyric, lactic,
and acetic acids; abundant hydrogen is detected. No aero-tolerance.
Isolated from human infections, particularly those associated with the intestinal tract; empyema fluids; normal intestinal flora of
human infants and adults.
Culture supernatant fluids are nontoxic to mice. Cultures are not pathogenic in laboratory animals.
Isolated from human infections associated with the intestinal tract and from empyema fluids.
  1. N.A. Logan and P. De Vos, 2009. Genus I. Clostridium Prazmowski 1880. In: (Eds.) P.D. Vos, G. Garrity, D. Jones, N.R. Krieg, W.
    Ludwig, F.A. Rainey, K.-H. Schleifer, W.B. Whitman. Bergey’s Manual of Systematic Bacteriology, Volume 3: The Firmicutes,
    Springer, 738-828.
  2. Smith L.D.S. and Hobbs G., 1974. Genus III. Clostridium Prazmowski 1880. In: (Eds.) Buchanan R.E. and Gibbons N.E., Bergey’s
    Manual of Determinative Bacteriology, Eighth Edition , The Williams & Wilkins Company, Baltimore, 551-572.
Milk reaction is weak and variable. Meat digestion is negative.

Positive results for H
2 production (abundantly), substrate utilization and/or acid production from: cellobiose, fructose, galactose,
glucose, inulin, mannitol, mannose, salicin, sucrose & trehalose.

Negative results for casein hydrolysis, gelatin hydrolysis, H
2S production, indole production, lecithinase, lipase, nitrate reduction,
starch hydrolysis, Voges-Proskauer test, substrate utilization and/or acid production from: adonitol, amygdalin, cellulose, dulcitol,
erythritol, esculin, glycogen, glycerol, inositol, lactose, maltose, melezitose, melibiose, rhamnose, sorbitol & starch.

Variable results for substrate utilization and/or acid production from: arabinose, raffinose (weak), ribose, sorbose & xylose (weak).
Clostridium innocuum
(c) Costin Stoica
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