Bacillus cereus - causative agents of food toxic infections
Last reviewed: 23.04.2024
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An important role in the etiology of food poisoning is played by Bacillus cereus. B. Cereus - Gram-positive, forming no capsule bacteria measuring 3-5 x 1.0-1.2 mm, mobile (peritrichous) or stationary. Cells tend to be arranged in the form of chains, on the stability of which the shape of the colony largely depends - it varies greatly for different strains. Form the ellipsoid spores, which are located centrally, but do not expand the cells. Bacteria grown on glucose agar at an early stage of growth contain lipid inclusions in the form of droplets (poly-b-hydroxybutyric acid), as well as often grains of volutin.
B. Cereus chemo-organotrophs, aerobes or facultative anaerobes, are able to grow in the column of anaerobic agar. The content of G + C in DNA is 32-37 mol%.
They are usually catalase positive. Restore nitrates to nitrites; ferment glucose, maltose, often sucrose with the formation of only acid, without gas; Do not ferment mannitol; form acetoin (positive test of Foges-Proskauer), lecithinase, grow on citrate medium, and also in the presence of 0.001% lysozyme. The temperature optimum for their growth is 35-45 ° C, the temperature range of growth is 10-45 ° C. Synthesize and secrete hemolysin, exotoxins; enzymes lysing bacterial cells, proteolytic enzymes, phospholipase C, some strains on medium with starch and iron form a red pigment, some - in different media fluorescent yellowish-green pigments. For growth, different strains need one or more amino acids. On a dense medium, colonies are formed, depending on the stability of the arrangement of the cells in the chains, different forms. In some cases, dull or in the form of frosted glass, colonies with wavy margins, which do not have shoots, are formed. In other cases, the colonies have root-shaped processes widely spread on the surface of the agar. The shoots can either be in the form of disordered plexuses, or be bent in different strains in a clockwise or counterclockwise direction.
On the yellow-salt agar with polymyxin B. Cereus forms waxy colonies with cut edges, surrounded by iridescent whisk (a positive test for lecithinase). Habitat - soil, water, vegetable substrata.
B. Cereus is very similar in its properties to B. Thuringietisis and differs from it by the absence in the cells of crystals of toxic proteins.
According to the O-antigens in the group B. Cereus B. Thuringietisis, 13 serotypes were isolated. They also differ in their H-antigens.
Some strains of B. Cereus are pathogenic for humans and animals. In particular, the role of B. Cereus in the etiology of food toxic infections has been established. Pathogenicity of B. Cereus is associated with its ability to synthesize and secrete two exotoxins. One of them consists of three protein components, has diarrhea, lethal activity and increases vascular permeability (diarrhea-lethal toxin). The second toxin - Cereolizin - causes a cytolytic and lethal effect and also disrupts the permeability of blood vessels.
Getting into food, pathogenic variants of B. Cereus multiply in them and produce exotoxins. Under the influence of proteolytic and other enzymes secreted by B. Cereus, various toxic substances (ptoamines) accumulate in the products. All this combined and leads to the development of food poisoning. Infection occurs most often with the use of B. Cereus infected plant products and milk (40-55%), as well as animals (25%) and other products.
When bacteriological diagnosis of such food poisoning, it is necessary to pay attention to the quantitative content of B. Cereus in products (10s-10b and more cells per gram), their isolation from faeces and washing waters in large quantities, simultaneous isolation from several people in group poisoning and t Serological confirmation of the diagnosis is given by the detection in the serum of antibodies to B. Cereus and the growth of their titer.
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