Biol/CSES 4684

CLOSTRIDIUM

SOIL MICROBIOLOGY

This webpage was created by Sarah Hammond

1. IDENTIFYING CHARACTERISTICS

Obligate anaerobe.
Relatively large rods.
Form terminal or subterminal spores.
Most cells stain Gram positive.
Most species are motile by peritrichous flagella.
Some species are capable of nonsymbiotic nitrogen fixation.
Fermentative metabolism.
Low levels of G+C.
Produce wide variety of extracellular enzymes.
Colonies tend to swarm on agar plates.
Most species are saprophytic, but a few are pathogenic.
Found in soil and in the gastrointestinal tracts of animals and humans.

The picture at left shows a Gram stain of C. tetani under bright field microscopy (100X).

2. TAXONOMIC DESCRIPTION
Clostridia are able to ferment several organic compounds. The end products include butyric acid, acetic acid, butanol, acetone, and large amounts of carbon dioxide and hydrogen gas. Clostridia as a group contain more different enzymes than bacteria in any other genus. These enzymes allow the bacteria to break down large biological molecules and therefore have a large role in biodegradation, the carbon cycle, and pathogenicity.

Most Clostridia are saprophytes, including those that are pathogens. Those that are pathogenic tend to be opportunistic. A few are serious only because of the virulence of the toxins produced (as is the case with C. botulinum and C. tetani), and a small number of cells may produce sufficient toxin to cause clinical disease and death. Most species are obligate anaerobes, although some are falcultative (C. tertuim, C. histolyticum). They typically stain Gram-positive with the exception of a few which are Gram-negative. Many species can easily lose the Gram-reaction altogether.

There are nearly 100 species identified. These are classed in several ways, the foremost being morphological and genetic differences. For example, typing may be based on the position of the endospore on the vegetative cell (ie; whether it is terminal or subterminal). Some are grouped together by their end products of fermentation, or by the enzymes they produce. The species C. botulinum contains strains that are not genetically similar, but they produce similar antigenic types of toxin and so are classed as one species.

3. ISOLATION AND ECOLOGY
Clostridia grow very well on CDC anaerobic blood agar (incubated in a GasPak jar at 37 C). Some other selective media include Prereduced Chopped Meat Glucose medium, BHI (brain-heart-infusion) medium, and McClung-Toabe egg-yolk agar (incubated in a Bio-Bag). The plugs to any tubes used for incubation must be clamped on or the amount of gas produced will cause them to explode off, and the influx of oxygen will kill the culture. The egg-yolk agar is selective for lecithinase activity, which is a major toxin produced by C. perfringens (the causative agent of gas gangrene). C. perfringens also produces butyric acid and cultures may smell like rancid butter. Because of their peritrichous flagella, colonies grown on agar will "swarm," or slowly migrate across the plate.

Clostridia are found in virtually every anaerobic environment containing carbon. This includes aquatic sediments, soil, gastrointestinal tracts, and even human skin in some cases (though the latter are facultative). Of the known species, a little more than 25% are recognized as having caused or contributed to disease. Clostridium species are well-known for causing tetanus, botulism food poisoning, gas gangrene, gastroenteritis and necrotic enteritis in humans. Some species are important in soil microbiology for their ability to fix nitrogen independently from plants. Still others are important in food microbiology because they cause putrefaction of meat, or ferment lactose in milk. Some are useful industrially for the production of butanol, and acetone (especially C. acetobutylicum).

Clostridium prefers anaerobic soils and is probably the most common Gram positive organism found in such soils. Bacillus, a relative of Clostridium, is the aerobic Gram positive spore-forming counterpart.

The above picture shows C. perfringens on trypticase soy - sheep blood agar.

4. ADDITIONAL SOURCES OF INFORMATION
Baron, S., R.B. Couch, D,W. Niesel, and G.L. Woods. 1996. Medical Microbiology. Fourth Edition. University of Texas Medical Branch at Galveston. 262-276 pp.

Elmer, G.W., and L.V. Mcfarland. 1997. Pharmaceutical Probiotics for the Treatment of Anaerobic and Other Infections. Anaerobe, v3, n2/3, April/June. Academic Press. 73-78 pp. (IDan960062).

Antoniads, G., C. Papadopoulou, E. Stoforos, and E.Xylouri. 1997. Rapid Identification of Clostridium perfringens in Animal Feedstuffs. Anaerobe, v3, n2/3, April/June. Academic press. 191-193 pp. (IDan970100).

Holt, J.G., N.R. Krieg, P.H.A. Sneath, J.T. Staley, and S.T. Williams. 1994. Bergey's Manual of Determinative Bacteriology. Ninth Edition. Williams and Wilkins. Baltimore, Maryland. 787 pp.

5. LINKS TO OTHER SITES ON CLOSTRIDIUM
Pathogenic clostridia

Clostridium isolation