BACILLUS

110 plus species including:

SPECIES

Bacillus anthracis
Bacillus cereus
Bacillus circulans
Bacillus coagulans
Bacillus laterosporus
Bacillus licheniformis
Bacillus macerans
Bacillus megaterium
Bacillus polymyxa
Bacillus pumilus
Bacillus schlegelii
Bacillus subtilis
Bacillus stearothermophilus

MICROSCOPIC APPEARANCE

Gram Stain: Positive and variable.
Morphology: Rods. The vegetative cells are straight, round-ended or square-ended rods.
Size: 0.5-1.2 by 2.5-10.0 micrometers.
Motility: Most species motile by peritrichous flagella.
Capsules: No.
Spores: The endospores are oval or sometimes round, cylindrical or kidney shaped and are resistant to adverse conditions. There is not more than one spore per cell and sporulation is not repressed by exposure to air. Location of the endospore within the cell may be central or terminal.
Other: They occur singly or in chains that range from a few to many cells in length.

MACROSCOPIC APPEARANCE

Typical Bacillus spp. exhibit large, flat colonies on non-selective media. They are often beta-hemolytic. Non-typical Bacillus strains may be very small and spore formation often fails to occur. Most do not grow well on enteric agars.

METABOLIC PROPERTIES

Aerobic or facultatively anaerobic, depending on species; respiratory or facultatively fermentative; most species chemoorganoheterotrophic; many can grow on Nutrient Agar; some species (e.g. Bacillus polymyxa ) can fix nitrogen; Bacillus schlegelii can grow chemolithoautotrophically.

KEY BIOCHEMICAL REACTIONS

Catalase-positive.

HABITAT

Present as saprotrophs in soil and water; also, found in decaying animal and vegetable matter.

PATHOGENICITY

Many Bacillus species have little or no pathogenicity and are rarely associated with disease in humans or lower animals. Exceptions to this are Bacillus anthracis , Bacillus cereus and Bacillus subtilis . Some species are insect pathogens.

B. anthracis is the best known pathogen in the genus; some regard it as the only mammalian pathogen. It is an important pathogen of farm animals, although in developed countries anthrax is of small consequence. Recent isolation of a penicillin-resistant strain of B. anthracis should, however, serve as a warning that this organism should not be treated lightly. (2)

B. cereus is the causative agent of more or less severe infections of both man and other mammals. This organism causes two types of food poisoning - an emetic type and a diarrheal type. Other Bacillus species thought to be involved in mammalian infection have been linked to corneal ulceration, septicemia, infected sites of melanoma, pharyngitis, endocarditis, pneumonia, respiratory disease, and with another organism, psoriasis.

RECOMMENDED MEDIA

For culture: Blood Agar 5%, Tryptic Soy Agar (TSA), Brain Heart Infusion (BHI) Agar, or Nutrient Agar.
For selective isolation: No selective media for Bacillus spp. other than Bacillus anthracis . Media for the isolation enumeration of Bacillus cereus in foods have been described. (4)
For maintenance: Blood Agar 5%, Tryptic Soy Agar (TSA), Brain Heart Infusion (BHI) Agar, or Nutrient Agar.

INCUBATION

Temperature: 25-20 degrees C. (food spoilage), 35 degrees C. (clinical material), 55 degrees C. (thermophilic organisms)
Time: 18-36 hours.
Atmosphere: Aerobic.

REFERENCES

1. Holt, J.G., et al. 1994. Bergey's Manual of Determinative Bacteriology , 9th ed. Williams and Wilkins, Baltimore, MD.

2. Holt, J.G., et al. 1986. Bergey's Manual of Systemic Bacteriology , Vol. I & II. Williams & Wilkins, Baltimore, MD.

3. The Oxoid Vade-Mecum of Microbiology . 1993. Unipath Ltd., Basingstoke, UK.

4. Murray, P.R., et al. 1995. Manual of Clinical Microbiology , 6th ed. American Society for Microbiology, Washington, D.C.

5. Internet: www.hardlink.com /Bacterial Database Search, February, 1998.


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