bacillus


bacillus
/beuh sil"euhs/, n., pl. bacilli /-sil"uy/.
1. any rod-shaped or cylindrical bacterium of the genus Bacillus, comprising spore-producing bacteria. See diag. under bacteria.
2. (formerly) any bacterium.
[1880-85; < LL, var. of L bacillum (dim. of baculum) staff, walking stick]

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Any of the rod-shaped, gram-positive bacteria (see gram stain) that make up the genus Bacillus, widely found in soil and water.

The term is sometimes applied to all rodlike bacteria. Bacilli frequently occur in chains and can form spores under unfavourable environmental conditions. Resistant to heat, chemicals, and sunlight, these spores may remain capable of growing and developing for long periods of time. One type sometimes causes spoilage in canned foods. Another, widespread bacillus contaminates laboratory cultures and is often found on human skin. Most strains do not cause disease in humans, infecting them only incidentally in their role as soil organisms; a notable exception is B. anthracis, which causes anthrax. Some bacilli produce antibiotics.

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      (genus Bacillus), any of a group of rod-shaped, gram-positive, aerobic or (under some conditions) anaerobic bacteria widely found in soil and water. The term bacillus in a general sense has been applied to all cylindrical or rodlike bacteria. The largest species are about 2 μm (micrometres; 1 μm = 10−6 m) across by 7 μm long and frequently occur in chains. Bacillus species form dormant spores (endospores) under adverse environmental conditions. These endospores may remain viable for long periods of time. Endospores are resistant to heat, chemicals, and sunlight and are widely distributed in nature, primarily in soil, from which they invade dust particles.

      Bacillus cereus sometimes causes spoilage in canned foods and food poisoning of short duration. B. subtilis, also widely disseminated, is a common contaminant of laboratory cultures (it plagued Louis Pasteur in many of his experiments) and is often found on human skin. Most strains of Bacillus are not pathogenic for humans and only infect them incidentally in their role as soil organisms; a notable exception is B. anthracis, which causes anthrax (q.v.) in humans and domestic animals. B. thuringiensis causes disease in insects; B. thuringiensis insecticides are harmless to vertebrates but effective against pests of agricultural products. Medically useful antibiotics are produced by B. subtilis (bacitracin) and B. polymyxa (polymyxin B).

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